For codes, sign up for the Dealflyer. It appears you get better offers after you've been a customer for a while, but who knows if that is true.
There are sometimes codes on the back of the mailings they send.
Codes are mostly one-time use these days.
I don't work for STP but can only guess that if they ever restock, it would be next November or so, as they this was the second year they rolled out the boots just in time for winter.