Long story short
A " LOT " of websites uses HAporxy as Load balancer so it have a proxy feature too!
Search google for
intitle:"Statistics Report for HAProxy"
And you will get a ton of proxies to figure out the port and you got free http proxy! and it’s blazing fast
Also if you use your mind you can write sample python crawler and get the results in txt file can be used for any port checker Nmap for example!