According to the Swiss Confederation website, the Cantonal authorities are responsible for this. See link, to all the canton offices, it says you need to contact the one in where you intend to live. See below. In any case you will likely need proof of support and swiss insurance during your stay.
6. Long-term residency in Switzerland (more than 3 months) / Employment in Switzerland
I would like a residence permit for Switzerland for more than 3 months
Due to a division of jurisdiction between the cantons and Confederation, cantonal migration authorities are responsible for issuing residence permits. Therefore, please address your inquiry directly to the migration authority responsible for your canton of residence. You will find a list of our cantonal migration partners in the following link (list available in German only):
Cantonal immigration and labour market authorities