I had an idea recently, it's basically a medium site to list your trades. You could create a trade with the cards you own and the ones you want, then it would be displayed on the trades page.
You could search for one specific card and see what the other person is looking for. Trades would get more attention compared to the currently in game chat, due to the cards being instantly displayed, and players could filter only the cards they want.
I worked a bit on it and came up with some mock ups that I'll post below. If you guys are interested let me know and I'll work on