I can't remember offhand if that chip can be paralleled (I think there was a recent post about it though, try a search),
but if so then you could up the current handling - but you'd not have the ability to use constant current drive from a
high-voltage supply (which is needed for high-speed operation). If high-speed isn't a requirement it sounds a possible
approach (given my first comment). [ just for completeness L6208's cannot be paralleled ]
There are higher current H-bridge modules available, such as the Pololu ones.
BTW do we know the winding resistance for the motor?