Hi.

I often rent apartments in the alps during the winter season.  I find the best times to rent are during the months of Jan or March, it's much more difficult in February as it's school holidays.  I think the best way to go is to decide on your resort of choice e.g. Morzine, Chamonix, Les Carroz, Courmayeur, Crans Montanta, Verbier and so on (cheaper in France though) and then find the webpage for the resort, search under accommodation and find the 'agences immobilier'  for the resort. Draft an email and then cut and paste it to each of them specifying the dates you're interested in, the number of persons, etc.  The closer you are to your date of depart the better, as they are much more likely to rent for a weekend then (cutting their losses).  It's a bit of work but it can pay off!  Good luck!