Visit any market of your area selling HVAC stuff.
Robinair, though expensive, is one of the best brands. Fakhri Brothers are authorized dealers for robinair and also for some orher related stuff like Honeywell refrigerants, Sunoco oils etc.
Apart from robinair there are many Chinese brands available in the market. Value is one of Chinese brand having good reputation and with a long list of AC servicing quality tools and equipment.
There are two kind of pumps available in the market, single stage and double stage and all are categorized in terms of vacuum flow rating i.e., CFM (cubit feet per minute).
Try to buy a two stage pump with atleast 3 to 4 CFM, this will perform its job in much less time than the lower category pump.