It depends on what voltage and current you want/need for your particular motors. Here are a couple of links:
Granite Devices VSD-XE, drives brushed and brushless motors at <160V and 40A peak.
GeckodriveG320, G320X & G340, all <80V, 20A brushed DC drives.
CNCDrive has two drives, one <80V, 20A and one <160V, 35A.
Larken Automation, two models, <95V/12A and <170V/20A
Semis in Bulgary has a range of servo drives and amplifiers, all the way up to 200V/50A peak.
All of the above take step & direction directly from Mach3. There are more manufacturers and models out there but these are the ones I can come up with at the moment that takes step and direction.