You don't need to trade - just cut them to size! I actually normally buy 28 pin sockets, and cut them to the size(s) needed. Just take your wire cutters and squeeze them on the socket on either side... eg if you need 2 8 pins you could do something like
0-0-0-0-X-0-0-0-0
| |
0-0-0-0-X-0-0-0-0
Cut where the X's are. Hope that makes sense. Maybe I should post about it on the blog.
-Colin