Getting Proxies for Your Proxy Group
This is the easy part. It may be tricky to really build up your group, but getting the daily list of proxies is easy. The only real trick to this is that you can't just grab the first page of results for "proxy" and call it a day. The first several pages of web proxies are already blocked. You need to find the new ones that are still unknown to the filters. Proxy life cycles are very short and you have to be ready to constantly update.
One easy way is if you're running both sides of the equation. If you're running your own proxies, then you can easily just start up a new one each day and list it. This is actually a good idea for a fairly easy web business. It won't make you rich but a few proxies and some free advertising can earn a pretty penny.
If you don't have your own proxies, then you'll need to look for others. You can always take the easy way out and take the results from other groups and directories. The only real trick is that you have to look for a slightly remote list, since you run the risk of advertising blocked proxies. This is naturally a bad thing.
The ideal way is to just ask though. You can go to any webmaster forum (Digitalpoint is a good one) and you can look for a proxy discussion thread. Join the board and post an honest request for proxies for your google group. Most people will be more than happy to give you some links. I saw this exact thing happen on Digitalpoint just a week ago, so it's still a viable strategy. The great news is that you can even work your way up to selling listings in your group. Once you've built up a membership, you shouldn't have a problem selling listings in your group for less than a dollar or so. Again, you won't get rich, but it's a good business option.