As a privacy service we maintain a very small pool of IP's per server, usually 3-5. We need to keep the number of IP's low to ensure sufficient interface crowding on the servers. Crowding is used to increase the total number of users sharing the same IP,  which combined with encryption makes it harder for a 3rd party to attribute an outgoing connection to an incoming one. If you are looking for a large pool of IP's then you may be better off with a proxy service that specializes in this type of offering.