Http Proxy Scanner is the software that helps to find HTTP proxy servers. 
It can scan up to 10,000 IP addresses per second.

License:  Freeware.

Installation and use:

1) You must have administrator privileges
2) Install "Http Proxy Scanner\WinPcap\WinPcap.exe"
3) Run "Http Proxy Scanner\Bin\HttpScanner.exe"

Attention:
The Program does not work with PPP/PPPoE/PPTP/L2TP connection directly (Modem, ADSL, WiFi, VPN) .
You need to install the router and configure it for PPP/PPPoE/PPTP/L2TP connection, then connect computer to router by network cable.
If program does not work or work very slow, then you must disable all firewalls, antiviruses and ndis filters.