Well... there's the WCRPG. If you're using mIRC you can find them at #wcrpg in DalNet.
Also, there's this pretty new WC Rpg namely Wing Commander Frontier, which took place around the border worlds circa 2668. Their homepage is at www.wcfrontier.com (nice Flash anims) and their channel, also in DalNet is #wc:frontier
Actually I am in the proccess of making an RPG called Jump Interphase. It takes place during/after Prophecy and I've been making it for almost a year now because I want it to be perfect. So when it does come out I'll let you know.
You would certainly be welcomed to our RPG at http://www.blacklance.org. We have two divisions: a European and an American due to timezone spread. This way we can have two ships and more members can participate.
Connect to
18.244.0.114 port 2197
with a MUD or MUSH client. It's Wing Commander: Red Horizon MUSH, a roleplaying thing which uses Hspace as well as a lot of other stuff to be WC. You can be UBW, Kats, TC, or a privateer, pirate... etc... Join in. It's fun.