Just picked up my 795 two weeks ago from Big 5; popping its cherry next friday now that weather is perfect for outdoor shooting.
I got two spare mag's from Big 5 also, but had to go to two separate locations to pick them up.
Most Big 5's will have a 24-hour reservation on outdoors equipment - make sure to call in and reserve the mag, they tend to go fast. If you jawbone with the outdoors dept. employee, you can get them to give you information on when they are making their next PO to the distribution center, and what their order qty. is going to be. If they are really nice, they can look up stock in other local locations as well for you.
From my experience, the distribution center seems to only ship half of what the individual stores order due to high demand short supplies on .22 ammo and accessories.
But once you know when the order delivery is coming in, call them in the morning to check stock, reserve and then pick up in the afternoon. They have a pretty regular delivery schedule so its pretty easy to time it... the hard part is waiting in anticipation.