Several Autopage remote transmitters have been more difficult to get since that company was sold. We are not certain why, but the new buyer seems either unwilling or unable to keep replacement remotes in stock. Go figure. One would think that supporting their customer base would be a priority of the new owners.
The most recent Autopage remote to go on indefinite back order is a 5-button remote with FCC ID H5OT21. This is Autopage part XT-33. Fortunately, Remotes Unlimited has other replacement keyfobs in stock that will work as a substitute for this remote.