Where can I find a fat man and some mininukes because i didn't think there was a fat man until I saw a mod for one I've been looking but can't seem to find one

The wiki is the best place to check.

http://fallout.wikia.com/wiki/Fat_Man_%28Fallout%3A_New_Vegas%29

the fat man is amazingly fun in FO3 to bad i havent gotten round to using it in FONV yet so still have to go have some fun with it hehe ^.^