hi Lyle,
technical data is very hard to get hold of, you will be able to find some simple drawings of most things,
but like you say you will only get cad data/detailed info on comisioned gigs.
for all my personal work i just simply use googled photos. ive been constructing this old merc from just looking at photos:
http://img.i7m.de/show/driza.jpg WIP
also have a look at objects around you, sometimes even the most mundane of items can make a nice illustration.
get the screwdrivers out and take something apart and start measuring
a client once decided that i could not be trusted with all the technical info needed, so they sent the actual product (a washing machine) and i had to take it apart and measure every single part by hand!
i like to do everyday still life renders when i can to, its the perfect practice for a technical illustrator....
this weekends doodle.....
http://img.i7m.de/show/c3m6o.jpg (excuse the bad compression)
its excellent practice for your observational skills. perspective, proportions, texture and lighting skills shoud be constantly worked at
have fun