It just takes a lot of digging man. Sometimes samples wont necessarily be found in records, but rather even movies, television shows, and commericals. You could always try PMing Penacho and asking what the source is, and what he usually samples.
Lots of indie rock has stuff like this. Especially if you look up "post rock" or "post metal", those are basically genres that use rock instrumentation but don't follow the basic rock song structure. You'll find a lot of good spacey ambient sounding stuff to snatch. Lots of instrumental stuff with no or minimal drums.
Check out:
Mogwai
Mono
Sigur Ros
Explosions in the Sky
