I am searching for some sort of proxy forwarder that will keep a stack of other proxy servers and will distribute connections between them. It will accept connections as usual proxy server, but then will forward them to another proxy from stack. For example it will keep a connections count for every proxy from stack and will switch to another on connections limit. Is there some existing solution?
The rules here is usually don't give product recommendation.
However, you can get better google/search result using proxy load balancer.
You may post question again, after you choose a particular solution/package/product, and have difficult setting it up.