We rented from a place in the centre of Les Gets, there where quite a few shop choices though both there and in Morzine. Just do a google. General rule with this stuff in France is you’ll get a discount for arranging and paying in advance especially if rental is not at the weekend. Ask them to change the brakes round too (left/right/front/back is different in France).
How’s you’re French ? Best to google in French “morzine location vtt” for example “louer” is the word for rent btw
Intersport have rentals euro 99 / 89 for Gold / Silver DH bikes – I am sure you can find some cheaper