Shooter's Choice, in Waterloo, Ontario, lists Winchester ammo too. They say they keep it in stock. Cheap, it ain't though. $77.95 per 20 for the 200 grain ammo. Brass is a bit better at $52.95 per 50.
Your local gun shop can order ammo for you. Be prepared to pay up front.
It uses an RCBS #5 shell holder. Only cartridge that does, so that'll likely be an order thing too. Or a Lyman #18.
I have data if you need/want it. 200 and 220 jacketed and 187 and 255 cast with gas check. Cast bullets are Lyman #'s 350447 and 350482. They don't list those molds now though.
Finding bullets might be an issue. Hornady makes a 200 grain Interlock FP. Barne$ makes a 220 and 250 grain FNSP. No Sierra's, Speer's or Nosler's.