Champs choice has eley match (black box) and Rws target rifle for less than that. They are not tenex but u really don't have to shoot competition ammo. I think midway has a bunch about to come in soon too. Good luck and let us know what u think.
Eley is very high quality ammo from the UK. They specialize in match grade rimfire ammo. It is usually more expensive than your average rimfire ammo, partly because if their quality standards, partly because if exchange rate and import cost.
It may be available because not many people buy it in bulk due to the normal cost of it compared to other ammo when it is readily available. It may also be available because the UK isn't having a bunch of Internet panic buyers cleaning out their store shelves.
I've used Eley match pistol and rifle ammo and found it to be some of the most accurate ammo available.