I would suggest if you aren't able to procure these under defined H-Bridges then try out making your own, here is a very good tutorial >> http://www.bristolwatch.com/ele/h_bridge.htm using power Mosfet's.
also even if you want to use small hobby motors like the ones futaba makes and are also found with TAMIYA hobby kits(i have one of them)then in that case also they call for a lot of Amperage to be handled you have to use the D -cell method to calculate the H-Bridge value before buying or even making one.
You have to go like 1) Hold the multimeter at DC amp level and put the + lead and - lead of the multimeter with your motor leads and power leads.
- Hold the movement shaft of the Motor from front and do not let it move and power it
while the multimeter is there it will show you the STALL current for the motors you have and as per that you have to choose the building mosfets or ready made H-bridge IC's for your implication telling you the highest current soaking that can happen in the worst case scenario's.
I used 4 L293D's by STACK SOLDERING them one over one and thus multiplying there original power.
EDIT: Example of Stacking attached for your reference.
