I just purchased the Big Boy, I'm level 49 with over 10'000 caps after the purchase and I want to be able to use my Fat Man on a consistent basis, where can I find/buy mini nukes?

Not sure where you can buy them, but I get mines from super mutant suiciders.

I don't think you can buy them anywhere aside from the Prydwen. And I might be wrong about them being sold on the Prydwen too. I'm not sure.

Don't think I have encountered any place where they sell mini-nukes.

A couple of ideas tho....

Spoiler

At the crossroad with Milton General Hospital, Fallon's Department Store and West Roxbury Station, there will usually spawn anywhere from 1 to 3 suicider muties, be careful fast traveling there tho, as you can get sourrounded by them on arrival I haven't checked if the two mini-nukes in Dunwich Borer's respawns, but worth a try. Otherwise, any place with large mutie concentration is your best bet, altho, the crossroads mentioned above, is easy to get to.

Trashcan Carla (Sanctuary's main/only trader) has mininukes in stock occasionally. And if you build the Weapons Emporium (the Weapons, class 3 design that costs 3,000 caps + materials), they will also occasionally have a mininuke available. (Not sure if the smaller booths ever get them as well.)

Also, note the location where you find mininukes. Most of the time, when that location respawns, all of the scripted items also respawn. For example,

Another also, whenever you engage a Supermutant camp or base, they will usually have a Supermutant Suicider that charges at you carrying a mininuke which he intends to detonate while standing next to you. If you kill him before he reaches you without hitting his right arm, you will be able to loot the mininuke off of the corpse.

I think mini-nukes are intentionally very hard to find to prevent the player from using a fat man too much. so there's no really good way to get the ammo.

as others have mentioned, re-spawning site locations and super-mutant suiciders are the best sort, and to check ammo vendors when you can, but a steady supply I think isn't out there.

Aside from killing supermutant suiciders without leaving the crater, they are very infrequently available for purchase from certain vendors, like one or two in stock max. Your odds go up if you build level 3 weapons stores in multiple settlements.

I'm sure, this was the intention. But given that later on, you have artillery cover almost everywhere, the nukes pale in comparison anyway. At the later stages of the game, all heavy weapons are more or less redundant. I usually arm my settlers with that stuff.

The Fatman simply isn't viable for consistent use, you'll never get enough Mini Nukes for that. Instead, think of the Fat Man as the weapon that guarantees success against a tricky boss or similar. Like, the Courser that you get the Courser chip from, he can be quite insanely hard to kill on Survival.

But, if you insist, then kill off suiciders before they blow. Hit them anywhere except their right arm. And then just play the game for some time without using the Fatman, getting a Mini Nuke here and there. At some point, you can easily have 30+ Mini Nukes and then go on a nuking spree.

ATOM BOMB, BABY!!!

https://www.youtube.com/watch?v=KXSUEU7ISfQ

It's worth poking around the lower deck in the prydwen, underneath where teagan and the doctor etc. are as after you clear out fort strong they move the cache on board and you can find a couple nukes on top of the crates, oh and if you modify it with a mirv, aim high and you'll need to be closer than you think.

Insanely hard to kill on survival ? Maybe if you try to take them down on level ~15.

I've killed like 12 or so till now, 2 criticals to the head and bye bye Courser. They don't even get to spot me.

The only time I used a Fat Man indoors was in Fallout 3 in the Capitol building. That was the biggest room I have needed to use one in.

Use a missile launcher and reserve your Fat Boy for special occasions!

I've never really found the need for mini-nukes on a regular basis. They're fun for Behemoths and some legendaries, but they're a little OP for my taste. I prefer missiles - especially with a good scope.

Find a super mutant settlement and farm it ever couple days. It's good for scraps/caps and at least 1 mini nuke. I haven't really looked, but I'm sure you can find location that has more then one bomb runner.

Ever hear the joke about using Nuclear Hand-grenades? Same principle. The ONLY situation where you should use a MIRV Fat Man is identical to sniping at long range. (Preferably VERY long range.) Anything less than long range, consider switching to a quad-barrel Missile Launcher.

Yeah, now it's: oh look a suicder, I gotta be careful ... to not hit the damn bomb. I want it.

Yes, I'm obviously talking about the lower levels when you're supposed to meet that first courser, and not the higher level when everything in the entire game is a complete faceroll.

And I'm sure you're a super duper player, but kill 18 more of those coursers, and then we'll talk.

Well yeah, at lower levels almost everything is hard to kill, on survival. And at higher levels you don't need to be a super duper player to find the game easy, if you play a sneak character. I'm not even a regular gamer and this is the first game where I play stealthy.

And what happens after I kill 18 more Coursers ? Is there a trigger that makes them stronger or something ? That would be cool.