You just have to inspect them im pretty sure and it should tell you their inventory. The best place to find em is at trade hubs but you have to be in the right solar system.
I think the 48 slot fighters are also relics and don't exist anymore, I have one but after one of the updates it was...
I've got a 48 slot fighter, they're pretty easy to find if you unlock all the portal glyphs and use a portal to head to a solar system that has them.
There are plenty of references on the internet with portal glyph codes for finding what you want. Found an epic multi tool this way too