I've been playing 3 Card Magic since 2007. I've played on the Wizards of the Coast forums, another small forum, and various other places.
I attempted to find archives of the Wizards of the Coast community forums, the first place I am aware of that played 3CM. I personally played in 2007-2009, and was able to find a few threads on the internet archive, but not a full one. If you have any leads on this, please let me know.
After Wotc 24 seasons at No Goblins Allowed. Here is the last thread I found, which links to each previous one:
On MTG Salvation, there were "3 card blind" threads. I know little about these.