how can i purchase model 1625 apple tv channel indicator apple tv

If you want a new remote for your Apple TV box, then Apple sells that separately as well.

The previous black model has now been replaced with a new model, which is also compatible with the A1625 Apple TV (tvOS 15.4 or later*). Buy Siri Remote (3rd generation) - Apple Store online.

If you insist on the discontinued black model remote, then you’ll have to buy from some other reseller.

Replacement remotes will have to be paired to the box: Pair the Siri Remote with Apple TV - Apple Support.

If you are wanting to purchase a new remote then you can do so from Apple or an authorized reseller. If you are asking about something else please clarify.