You'd be best off to use a 36v 20 amps controller, though it will run perkier with a 30 amps.
You have to really watch overheating these motors, and yes, 36v 20 amps should get you to 20 mph. The original EVG had a controller in the 20 amps ballpark. I vaguely recall it might have even been less, like 18 amps or something. Look way way back in threads by Gmouchawar for the best info on this motor. I think there is a link to a manual in the tech reference section.
Regular brushed controller will run them. Scooter parts stores are often the place to find brushed controllers nowdays, or Ebay.