This question comes up on the Board now and again. Definitely not off-topic in my opinion. Here's a thread from about five years ago that speaks to the subject:
http://www.net54baseball.com/showthread.php?t=116547 Some good ideas within. Hopefully others will weigh in and update things.
In 2007 when I was there the one place that stood out from all the other stores was The National Pastime. Unfortunately they closed up shop several years back. All I saw otherwise was a lot of "manufactured memorabilia". There may well be an honest card seller or two. Others may be able to speak to that.
My wife and I dream of returning to Cooperstown someday. We had a wonderful time there. I expect you will too.
The National Pastime storefront (RIP)
