Where to find proxy lists?

I am spamming this forum in my niche and constantly need new IP addresses. I can't go and buy stuff from proxybonanza because I would still be limited to a small list of IPs.

I was wondering if anyone knows of a good source of proxy lists? I wouldn't mind paying for it.

Also, does anyone know how to use PHP to test the proxies and determine how fast they are?

Thanks.