B. I.
Google
If you want to buy an Annual Pass, you have to go to the Visitors Center first. Very helpful staff & management here - they can make things happen!
Also, insider information-the bus tours actually leave from one of the four "hotels/chalets" outside the park. They may can work a deal for you to be picked up at the Visitors Center instead, if you are rolling in with a rented RV and a multi-night stay.
We had to split our party of 4 in half to do the tour, but it beats traveling 1500 miles and not getting to experience the heart of what you traveled to see!
Beer, eggs, cheese, Cokes, stoves, TShirts, ice cream, coffee, etc. are all sold here. This place caters to the campers, hikers and the tourist here.