All relevant data in one page, also with data for other currencies:
https://zkb-finance.mdgms.com/home/bonds/index.html
SNB policy rate, SARON
Calculator for a Compounded SARON
Swap Rates
If you have better sources, feel free to edit this post.
ZKB page have no history, or at least I havenât find it. But I trust it more wrt correct current values.
investing.com has historical data, but the values seem to be slightly off. So I look at it mostly to check the time development.