My recommendation would be to try the ABRSM syllabus.
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This first list takes you from basically open strings all the way to pieces like the Bottesini Reverie and Eccles sonata and is mostly graded sensibly I think.
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By the end of this second you're looking at mad stuff like the Jean Francaix and Peter Maxwell Davies concerti as well as the Bottesini virtuoso pieces, but I find the ordering with regard to difficulty somewhat less organised here. Certainly the first list is a good one to consider, and the second, well, use your discretion. I'd never actually heard of a couple of the pieces on the second one when I found it, but there you are.
Alphonse Leduc do have a list of difficulty, -but- I think it's worth noting that they are an expensive company to buy from. I think all the 'standard' pieces they sell (Dragonetti concerto, Bottesini concerto, and Bach) can be bought elsewhere for about half their price. Also there are some very strange and not altogether attractive pieces in their catalogue, I think there's a reason why people don't often play a lot of that stuff in recitals or record it to CD. The ones by Joly, Alain Weber, Julien, Fontaine I found to be particularly naff. Avoid. Some nice ones are the Gouinguene Adagio (think about the same kind of level as the slow movements from baroque sonatas like Marcello), The Serventi Largo et Scherzando is worth a look too (more complicated, and you'll need a damn good pianist too! I played this in a first study piano accompanist master's exam there was so much for her to do) and then the aforementioned Desenclos piece which is great. Bigot Capriccio is a good one too, but more towards the virtuosic end of the spectrum.
Tends to be the main issue with these french pieces, they're all a bit 'interesting' - they sound great but the writing is typically not very idiomatic, the harder ones are typically full of passage work you'll have never seen the likes of before and probably never will again. I find it takes a lot of head-scratching in order to figure out how the hell you should play the notes in a sensible way. That might just be my own personal failings speaking though. I suppose that's a good thing and a bad thing depending on how you look at it, how much time you have etc.
Sorry for the rambling, but just thought I'd say a bit about that french stuff, some of it is quite rewarding in its own way yet in my experience people just don't seem to know a lot of it exists.
