Welcome to France !
The updated list of all transponders and repeaters (VHF, UHF, D-star ..) in France is here: https://www.radioamateur.org/relais/ (click on repeater for more informations)
(site web : www.radioamateur.org rubrique : Relais VHF/UHF France)
On VHF, the simplex calling frequency is 145.500 (FM) (channels simplex : 145.500 to 145.550 with space of 12.5kHz)
on UHF : simplex calling frequency is 433,500 (FM) (simplex : 433.400 to 433.575 with space of 25kHz).
But beware ! There are not many OMs on these bands especially very early in the morning! So a VHF / UHF activation may not to be possible.
Instead, a transceiver like the KX2, lightweight, with little current required, can be provided for activation on HF bands.
Don’t forget to post alert on Sotawatch right now.
Also beware of cold and wind, even if the weather is sunny, even in summer, temperatures are usually below 0 ° C.
Keep the battery warm under the jacket +++ to avoid freezing.
Also don't forget about booking the shelter because there are many and many alpinists who climb the Mt Blanc.
The day before, it is necessary to leave very early to have a good place in the shelter and avoid the falls of stone in "Le Grand Couloir" (under l'Aiguille du Gouter).
Be careful when crossing it, it's the most dangerous part of the ascent. The beginning and the end are protected, and it is necessary to check +++ that there is no fall of stone before crossing (duration of crossing : 30 seconds approximately).
Don't hesitate to contact me for more information.
Enjoy your stay in French Alps, it's a very beautiful country