Stores Amain Hobbies has a lot of options but they don't carry all the bodies from every manufacturer. Island Hobby Nut also has a bunch of body options.
The stores can't carry all the bodies from every manufacturer and it's good to check their website directly.
Manufactures Pro-Line Racing is popular and there are some bodies that you won't see on Amain as well. The same could be said for just about any manufacturer. Delta Plastiks. They have some pretty nice options. Injora has some nice Hard Body options for crawlers.
Of course there are factory bodies and custom options too.
There are probably 100 more sites that I don't know about. Figure out what you want then start searching for it.
OK that makes it more interesting. That's something you'll need to figure out. I don't have one to look at, but I would guess there would be some posts near the shock towers. Maybe you can look at the base camp part list?
There are also other methods like magnet mount, velcro, or you might be able to reuse the under body clips. Maybe some 3D printed parts for the new body would help. You might look around on YouTube and see what others have done.
That's perfect if you prefer the body posts. The probably drop into the cross brace on top of the shock towers. You just need to figure out which ones fit the new body the best. Then cut some holes for them.
There are lots of YT videos on cutting body holes.
If you want to get fancy you can get magnets for the top of the post. Then glue magnets to the underside of the body. Again check out YT.