No. 7x57 ammo should be fairly easy to locate in any good gun shop. There just isn't a lot of variety in ammo for the 7mm Mauser. Federal, Remington, and Winchester all make a 140gr. load for it, and last I looked Federal still made a 175gr. loading. PMC also makes loads with both bullet weights.
If you can't find ammo locally, you can usually purchase via the Internet from several
suppliers, including one custom ammo mfg. I know of. Following are a couple of links:

Cheaper Than Dirt: http://www.cheaperthandirt.com/ctd/default.asp

Midway USA: http://www.midwayusa.com/

AmmoMan: http://www.ammoman.com/default.htm

Conley: http://www.cpcartridge.com/index.htm