I had exactly the same thought - dark eldar on ruined craftworld bases. I also had a long look around the net, and couldnt find much. I considered these for a while, though:
http://dragonforge.com/Painting%20service/for%20sale/base_sets/sci-fi/Lost%20Empires%20Series.htm
As I happen to also have a craftworld eldar army, I had lots of bitz that were useful. I ended up hand sculpting 10 x 25mm bases, 5 x 40mm and 3 x 60 mm bases, then casting them up in resin myself. The resin and silicon (for moulds) cost about as much as buying the bases for my army would have cost (about a hundred dollars, for about a hundred bases, including several big 'uns), so its not a money-saving method by any stretch. I did buy quite a lot, though - 2 litres or so of resin.
One big advantage of this method is that I could incorporate GW eldar bits into the bases, which is something no online seller of bases can do (IP copyright infringement is something GW are red hot on.) I also only used about half of the resin/silicon I had bought, so I can do some more funky stuff with it should I get ideas in future. Another advantage was, well, they were my bases. Nobody else has em. I like unique stuff, so sue me
The cons of self-casting are: its not cheap, and you have to measure the resin/silicon pretty carefully or Bad Things happen. A scale that measures in grams is dead handy. There's also the issue of sculpting your own bases. If youre not able to sculpt, then clearly its a bit of a non-starter. If you can, then you should give it a shotty - resin casting and moulding is actually pretty easy, for bases at least. Anything with a large, flat side is no problem. Fully 3d things get a lot fiddlier.
So, aye - I hope that helps. Basically, you can either compromise and get "generic alien civilisation" bases, due to GW's stomping of any online retailer that looks too "eldar" or you can make your own. Good luck!
