I have two 42's inherited from my Grandfather. Neither one runs right now. One is reasonably complete , but has a bad gear in a motor and a short in the wire harness, the other is a complete basket (more specifically shoebox) case, totally disassembled (that's the way I got it).
You'll need to remove that modern pickup plate and look inside. There are enough images of 42's on this site to get a decent idea of what's supposed to be there. Greenburg has a prewar parts book that's reasonably helpful, also there's a good detailed writeup of a 42 restoration on the TCA ETrain site.
I've found and bought some used motor parts at larger train shows. Chances of finding motor parts on-line are probably slim, but do your best to turn it into a runner and not a shelf-queen.