I noticed this tidbit a while back when doing runs between spawn points aka was looking for lvl 4 vendors to recruit, long story short I found out the hard way they wont actly show in town.

but back on topic if u run across manta man you can ether steal or kill and loot a junk jet from him.

ive killed him 5 times so far with 5 different games so I'm thinking the drop is static

I didn't choose bos as my faction so this helped me out as normally id never get the opportunity to have this fun gun.

Technically, you don't have to join the BOS to get the junk jet. You can do Arcjet with no commitments, grab the junk jet during the quest, and after when Danse tries to recruit you into the BOS you can tell him no.

I've done at least five characters and have never seen Manta Man, but I've run through Arcjet every time (lots of loot early game and Danse does all the work). According to the wiki Manta Man is a random encounter and only shows up if you do the Silver Shroud.

i stand corrected what i ment was if you missed it during the quest as im unclear if u can get it beyond that point so this is an alternative