I use a Brno 21H in 7x64 and love it. I have bought several bags of new Remington brass for it from Wholesale sports in Saskatoon, from a production run Remington did a few years ago. You might find more kicking around, but not in the Saskatoon store. It was good and cheap, a nice combination! I have also bought new Norma brass, available anywhere that sells Norma ammo. I especially like RWS ammo and brass - it costs about triple other stuff but is very high quality.
from what I read, most 7x64's shoot heavier bullets better than lighter, think 160 - 175 grains as optimum. But mine shoots the RWS 8 gram (123 gr.) at 3100 fps accurately. So the 7x64 can also be super versatile, good for both far and fast for medium game at long range or heavy and deep penetration on the big stuff.
With the long throat in mine ( 0.33" ) I can load more powder than most manuals list for the same bullet weight in the .280, and get better velocity with no excess of pressure.
I killed one of my best bull elk with my 7x64 a couple years ago, and a nice mule buck this year.
since this picture was taken I had Ralf Martini replace the bolt handle with one of the Oberndorf style, added new shroud with model 70 type safety, and put a Leupold 2.5-8 on it with Talleys QD's. I really like the rifle and chambering! I'm sure you'll enjoy yours.