How to find ski lodging for a few weeks?

I’m looking to have 3-4 weeks vacation for snowboarding. I can go for both Hokkaido or Alps, as long as there is at least one big resort around.

Airbnb & booking.com prices are pretty high and certeinly not focused on weeks long vacations.

Does anyone have an idea how can I find a place for longer stays? Some Japanese website or any lead?
I can also offer a swap for my Tokyo apartment but not sure if house swapping is common here, and where can I look that up as well.

Any advice will be great!

Thanks