I prefer to carry a sidearm for quick access, the rifles would stay stowed--just my preference. If *it* is a threat, *it* will be too close to fumble for a rifle. Some folks could take assault weapons within view as an implied threat and it's contrary to being polite--and politeness will keep you have having to use the weapon to begin with

...Being in Arizona (you, I'm in NV), doing either wouldn't be a problem as it's not frowned on as much as some other places. Oh and to answer your question: check sporting goods stores, I see them all the time around here (even Walmart).
http://www.cheaperthandirt.com is a good place as well to look.