If you are hell-bent on finding your own proxies you basically have two choices:-
1). Scan the entire interwebz - any old port-scanner tool can do this, just set it up pointing at a range of IP addresses and the common HTTP proxy ports like 8080 & 3128. Be warned this can take forever, seasoned port-scanners learn where to look for proxies (clue: USA academic & commercial IP ranges are full of em). Even if you do find one you need to worry about (a) is it logging your IP and activity, (b) is it masking your identity (anonymous).