Do you have a local hobby shop that will take them? My local shop takes in parts, and offers modelers the opportunity to rummage through them for parts they need. It's a good service, and keeps everybody happy. I had three very large plastic bins worth (2x3x2 ft. bins) that were just taking up space a few years ago, so I took them in to my LHS. I kept a couple of small shoe boxe sized bins of figure parts and various "do-dads" of engines, weapons and detail parts, which I sorted into one of those stacked organizer type boxes with small drawers-- everything else went to the LHS. There is also an internet group called "Beyond the Sprues" which builds "what-ifs" and one-offs-- perhaps someone in that group might take them off your hands for postage. Here's the link:

http://beyondthesprues.com/Forum/index.php

VR, Russ