Midway usually has just about everything you will need for ammo or reloading. Oddly in this case they do not list any brass but only loaded rounds at an average painful price of about $125 a box. They have everything else for reloading just no brass.
I just did a quick google search and everywhere shows dicontinued or backordered. I'm sure it's out there you just have to find the right supplier or check some auction sites for once fired brass.
That's a big gun. What are you planning to go hunt with it?
If you're lucky enough to be on private land and can leave your stand up during the off season you can tie an old piece of cloth or something of the sort to your stand. I like to use an old camo bandana that I have. That way the deer get used to the movement and eventually don't bother even looking up when there is slight movement. This may just give you the time to draw your bow or raise your gun without being detected.