10mm brass unavailability is a relatively short-term problem. I suggest going to Starlinebrass.com and navigating to the "All Cases" page.
Click the notify me button. Before too long you will get a note that they brass is available to order. Buying directly from Starline is way to get the best brass at the best prices. Then order a 1000 or so and you'll be setup for a little while at least.
In the meantime, you might have to grab a box or two of factory ammo to get a small amount for your short-term reloading circulation.