You will need to buy online.
Get on Midway, Brownells, etc., make an account, and place the items you want on your wishlist. They will email you when it comes in, so make sure you have your email sent to your phone and check it twice daily. Midway says it'll have brass in by 2 March 2013, so you should be able to get something soon. I'd set a calendar event for that morning.
http://www.midwayusa.com/product/1601199429/remington-reloading-brass-7mm-08-remington
Also check web sites such as vaguntrader.com or equivalent for your state. Subscribe to the ammo forum and watch for brass. You'll just have to continually check. Save up your money while you wait. I would expect you can score 500 cases within 30 days if you really try.