Wasn't in Geneva so I can't speak to any local restrictions, but in the region I was in...
From a dealer as non-resident you needed to obtain a purchase permit good for 6 months or 1 gun (whichever came first). You had to apply for each and every permit at the local police. I found it very easy to get the permit for rifles. Never tried to purchase a handgun.
From private party as a non-resident you can purchase anything the other person is willing to sell you. They are pretty conservative with private sales though. The private seller shares the full responsibility and consequences if you do anything dumb with the gun after the sale.
For permanent residents "hunting rifles", which is just about anything from semi-auto to 50 caliber, you can buy from a dealer without permit. Handguns still require a purchase permit.
I would do your due diligence and double check with the local authorities though as it was pretty clear, at least the region I was in, that "common sense law" was followed more often than the way the laws were actually written in the books.
