I can't recommend Sport 2000. We've used them quite a lot and had big problems. Bikes either not what we asked for or in a poor state. To be fair though, they've massively expanded their bike shop area for this year and they might do a bit better – I need to go down soon and have a chat about their plans for this summer.
Twinner in Arc 1600 is better, although only used them a couple of times. They had Commencal stuff last year.
Mitch at La Grange au Skis in La Rosiere is excellent. For this year, he'll have brand-new Kona Stinkys or a couple of well-maintained Kona Coilairs. Good guide too!
Whichever option you go for, it will inevitably be expensive!