Yep you sure can buy them. Today, in preopening, the 1oz Maple leaf will cost you CHF 982, and they will buy it back off you for 910.
20 Franc Vreneli - they will sell it for 187 and buy it for 169.
The prices will change during the day. You could find the current prices around
here somewhere - look under Metals/Coins on the left.
I'd say bullion coins would be available from most branches with counter service. Just look for a sign with "Erdmetall" (?) or similar. CS would have them too.