You have probably already found the commercial sites that sell generic backgrounds. I think those who want a local and recognizable landscape either do it themselves or they contract someone, maybe a knowledgeable and skilled friend, to do it. Then, there are places that will make large copies for you, including Office Depot/Staples and others...but ask first if your closest place does that, or can.
A tip: if you decide to tackle this yourself, and a two-year-old cell phone will do a good enough job, find a location that will allow you to capture much of the local landscape, especially prominent features...BUT....here's the tip...DO NOT climb much in elevation to get 'more of it.' If you want some flat fields, even planted corn and stuff, if you climb more than about 20' the printed result pasted or mounted on your backboard/drywall will look like you have a tilted landscape, tilted and rising up toward a higher horizon than the area where you are. It might only be me, but I find too many look like that and they look goofy at best. Understanding that you are standing tall above your notional landscape on your layout, over your yard, tracks, and terrain, the lay of what is before you must match what lies 'beyond' the layout, that being your backdrop. I hope I'm making sense.
