Couple ideas here...
A large 5-star Hotel - Hotels host a wide variety of conventions, big enough places doing three or for cons at a time. If you were to have NRA, Anime, and Film cons on in the hotel, it could explain the presence of a wide variety of weapons and items (including the ability to have pop-culture joke items like a Master Sword, the M41a Pulse Rifle from Aliens, Rozen Maiden costumes, or anime wigs to pop onto zombie heads).
Vacation Resort - A fictional Mexican, Cuban, or Dominican resort would provide a very spacious exterior to run around in, large enough buildings to maintain internal levels, and a large cache of weapons could be explained away by "rebels" or the likes. Imagine the romance of strolling down the beech at night in Puerto Pollo, and by romance I mean terror, and by strolling I mean running for your life as undead crawl out from underneath the sand.
A School/College/University - Depending on what particular kind of school and where, there's so many ways to go with this. My vote would be for a highschool or junior-high in a similar town to Wilamette, again keeping the game in Colorado, and again not being in a real city. There's all sorts of weapon-like items in a school, plus guns taken from the students' lockers (would be taboo to do, which to me is all the more reason). The general premise for being in the school instead of wandering too far into the city could be tied to searching for someone/something.
If more a college/university approach I'd go with a real ivy-league school, old buildings and very victorian schoolgrounds. Give a bit of a res-evil creepiness to the place. And of course, there's the fun of it being in an elementary school. Being able to baseball-swing at zombie ankle-biters, but that would make it an AO game for sure. No matter which way you go, having a school means food on site, and a very steady supply of chairs/desks to beat zombies with.
A fictional parody of Alcatraz - Prison, but not just a prison. A prison that's on an isolated island with no way off. The outbreak occurs during meal time, the guards don't realize what's happening and think it's just a brawl when some inmates turn, and begin attacking others. This leads to infection of guards who break up the brawl, and the start of the game. The whole prison goes straight to hell, and unlike Dead Rising original, there is no set 3-days to the game. Not saying there wouldn't be story missions and possible endings, just that until you complete the required tasks, there's no help coming. So three ways to end it beyond simply failing/dying. 1 - Kill the exact number of zombies specified (X inmates + Y guards/staff - Z Survivors). 2 - Complete a certain story arc and find your way off the island. 3 - Complete a separate story arc which in the end causes the island to be napalmed. Choices throughout the game would determine the final path, and multiple possible endings depending on what choices were made. Also important for this concept, as you get closer to the final kill count, zombie populations become less and less. It would be important that the game doesn't render more zombies on screen than are remaining in the game. Also, as the numbers dwindle, something could be implemented to make them harder to kill, as well, only spawn a few of the remaining undead in each zone, so you have to go out looking for them.
Lastly, South Park Colorado - Dead Rising in South Park. Almost making a mockery of the animation, the simplicity of South Park style means we could have a Wii-compatible Dead Rising that doesn't equate to three zombie spawn limits.
