Instead of photo identification of the team/player it may be easier to track from the "researcher" side. Start with current owners acquisition:

1) Where did he/she find the postcard? Was it purchased from ebay/craigslist or an unrelated source? If so, what was the address of the seller? This should help narrow the area of focus.
2) Or, was the PC from a family collection? If so, what was their name (not necessarily a relative of the player, but a former teammate/classmate), and where were they from?
3) Since this is not an immediately, recognizable, professional or minor league team is it possible the PC is of a high school/college player? Honestly thought "masonic lodge" team when I first saw the logo.

Not saying impossible, but without more information it will be difficult. Really a needle in a haystack.