Any National Forest Rangers Station, Any National Park or Monument, many fee sites (like Mono Lake Tufas) also sell them.

I've had mine a while, but just picked up one for my GF, we had to call several Rangers Stations, because some Rangers Stations were out, at Arcadia for instance, and were waiting for more, we had to drive to Glendora.

In the Bay Area, try the GG National Park, at the main offices or visitors centers. I believe BLM also has them. These cover the stupid new National Forest "access" fees, imposed in improved National Forest locations, which was recently reinstated.

Since there is a rush on for all of us baby boomer old geezers to get these before they blow out the price, you should call and ask if they are in stock, so you don't have to waste a trip.