i had exactly the same problem as you unfortunately, i could find no french music to suit my taste. after hunting around a bit, i was told that the french do not apparently do alternative rock -___- i was peeved. i study french and german and german music is so good.
sorry to be incredibly unhelpful... but if you miraculously stumble across some french alternative rock please let me know ^u^
I don't know about France, but here in Quebec we're swimming in alt-rock bands. I don't know but the surface- Grim Skunk for a heavier sound, Les Georges Leningrad, Malajube, Karkwa, Les Breastfeeders, Les Colocs, Jean LeLoup. I'm sure there are tons more.
I understand! Well for the moment I mostly listen to French classics, but I'll let you know I find something , maybe someone here has already posted something? Sadly I haven't had the time to checked all the music here, yet.