Brass from shooters is getting hard to find since most of the folks are getting into reloading. I had the same problem with 340 Weatherby brass. If you Gioogle 264 Winchester you will find quite a few places that sell it and you can decide if it is in your price range.
Critter, Most places are on backorder for new 264 brass, I have a couple thousand rounds loaded but our prairie dog season is close so it won't last long. anyway I'm still looking for GOOD used brass if anyone has some they want to sell.
I cleaned out my local Sportsmans Warehouse when it was shutting down. But now that I think about it, I remember there being some at the Loveland store last week. If you're still looking, I can hook you up, assuming it's still there. PM me if you need it.
Understanding wind currents and thermals in hilly, broken terrain can often be incredibly frustrating. I've found that collecting and storing milkweed seed pods during the late summer has made me a better hunter in the bluff country that I hunt. These little feather like seed dispersers will float on the lightest of air currents and will show you what the wind is not only doing right at you're location but more importantly down range. I like to use the off season to float them...