I think you may have some trouble finding the numbers you are looking for, but there might be some sources that could give a good indication.
First of all, the number of available rooms for rent should be easy to find from the city. Often, these numbers are tracked by local municipalities because how many rooms and capacity have a lot to do with taxes and permits.
I would also contact the local ski resort, to see how many lift tickets they sell on the weekends, or if they track how many people visit the resort on the daily basis. If the resort is owned by a publicly traded company, this should be public information. But even if it's not, I think the resort would probably help you.
Another place to look is the city chamber of commerce, they may already have all of this information for you. City managers office as well, they like to know when there are rushes of people, for how long and how many people on average. This helps them budget for things like maintenance, as well as staffing emergency service.
I don't think you're going to get a lot of help from any businesses that sees your business as a threat. Like hotels. If I was one of those hotels, I wouldn't want a small operation to come in and undercut me, so I don't think I'd be offering up a lot of info.
I have a hostel, and a hotel, and am working on another hostel at the moment. When I work on numbers for a business plan, one thing I am sure to do is to not be over optimistic about my prospects. Be sure to be realistic. Don't bet that your first year open that you're going to be 100% full between Christmas and New Years, things like that.
You've got a great resource of knowledge on this forum, good luck!