Thanks for all the great advice!!
As Joe mentioned, it's really, really, really tough to get in touch with people on ebay unless you buy from or sell to those people. It was great, back in the day, when you could contact the winner of a big lot and ask if he/she would be willing to sell a piece or two from that lot. I understand why ebay made the instant communication impossible, but I sure do miss it.
As far as garage sales and local auctions, I guess I don't want to devote that much time. I
know my wife doesn't want me devoting that much time
. Since Salt Lake has never had a major league team, I'm not sure my time would be well spent.
The tip about picking up "trade bait" when you see it is a good one!