If you are talking about Quest 2 controllers, go to the https://www.oculus.com/quest-2/accessories
If you mean the CV1, Rift-S or Quest 1, ebay is your best chance since they aren't sold by Oculus anymore.
The Go controller is still available in some countries like Australia, but not America.
Rift-S and Quest 1 controllers may come back in stock, but I doubt it. The Rift-S was discontinued and the Quest 1 was replaced, so it's unlikely they are making more controllers. Oculus are probably keeping the remaining stock reserved for warranty replacements.