I'm not saying no one will do it, but you're asking for something that's a bit of a pain in the ass, and probably something that most providers could charge an extra amount for. You do realize if you use those proxies and get 1 of them burned that chances are you've also burned out the entire c-class with it? If you think someone is going to let you just run through ranges like that you're insane. Lol. I'm not saying you're going to get them all burned out or anything, but I think you might find it easier if you just asked for 5 or 10 proxies from each provider, and then asked them if they could make those all diff subnets.