I can't seem to find one anywhere. Are there any merchants who permanently keep it in stock?

the bartender at the mojave outpost normally has one

Try the vendor in Novac he usually has them in my game.

bigcrazewolf

If you can get your Science skill up to 100 (via skill magazines/Mentos/Lab Coat or natural leveling) i'd suggest performing the quest you can find at the NCR Sharecropper's Farm. Through the course of a quest, you'll come accross a detonator (among other select goodies) if you manage to unlock the Armory Door from the Overseer's Office.

Just... um... bring a Space Suit/Radiation Suit, and plenty of Rad-X and Rad-Away... you're gonna need 'em.

Also, Detonators are (in my experience) sold if a vendor sells C-4 explosives.

You can also shoot the c-4 to make it go boom.

bigcrazewolf

C4 is soo expensive.. I've never bothered to buy any C4 or a detonator. But I've seen the detonator at various merchants, try going through them all, some of them has one. But not until you have a big enough level I think.

I can think of at least two detonators placed in containers guaranteed to spawn. One at the NCR post between Novac and Nelson, in the little footlocker - the other in a hard locked briefcase on a table in the Lucky 38 Cocktail Lounge.

This..
The NCR post is the best one to get, if you're looking for a freebie.

I foundt my detonator sitting near some C-4. Probably in the Vault 34 Armory.


B)

Johnson Nash sold me mine in Primm, after it was all cleared of prisoners but before the sheriff was appointed. He also, unsurprisingly, sold C4.

you can get a detonator by helping the boomers. at the end of their final mission you get one that you can keep.