I see them once in a while on ebay usually for more than I want to pay. One thing I've read is that there are many 400/800 games that never made it to 5200, especially Imagic titles. Mainly, I would love to have the XE light gun for 7800 and the lone 2600 light gun game, but they rarely come up for sale.
Am I missing out much on the 80's gaming scene by not having XEGS? I have INTV, VCS, and CV as well, so aren't most of the XE games already covered with systems I already have?