You must be able to rent them all over.
Pezier sports in Argentiere (up the valley) do hire ABS and have spares too:-
620, ROUTE DU PLAGNOLET ARGENTIERE
74400 CHAMONIX MONT BLANC
Tél. : + 33 (0)4 50 54 68 48
info[at]pezier-sports.com
(replace the [at] with @)
I would have thought Snell or one of the other Cham3S shops would hire them too
SNELL
104/ 118 rue Paccard
74400 Chamonix
Tel : 04 50 53 02 17
Fax : 04 50 53 42 40
E-mail :
Let us know if you find out from snell and what the cost is.