I think that the people who live in tourist areas consider Labor Day to be 'Freedom Day' when they get 'their' bit of paradise back. They then revert to their normal winter lifestyle.
The stores that stock up for the summer trade will let their stock go back down to the winter level. Operating hours also may be cut back.
The main resupply location in Desolation Sound is Refuge Cove. They have fuel, propane, a grocery store, ice, government liquor store, Post Office, laundry, showers, hamburger stand, book exchange, chart sales, water to fill your tank(taste first!), and a large dock(often full in the summer) where you can stay overnight. They do not have garbage disposal facilities, because they are on an island with no ferry access.
The best plan may be to bring everything you expect to need and resupply your ice, fuel, and water as needed.
What about the garbage? Never fear, Squirrel Cove is across the channel from Refuge and has garbage facilities, store, and a very protected anchorage. At the back of the anchorage is a "reversing falls' into a salt water lagoon. If you go in in your dingy before high tide, you can ride the current in and when the tide turns, ride the current out again.