I'm pretty sure they aren't available from GM anymore.
You can find NOS and aftermarket switches on Ebay.You can also find new aftermarket switches in the HELP section in most part stores.
Billy-I have several used ones, also your local auto stores usually have new ones in help section for small parts, I have also found that taking them apart and cleaning them with a good electrical spray cleaner usually puts new life into them and they start to work once again.