So you just need a promini equivalent with an H-bridge chip?
Seems pretty straightforward.http://www.ti.com/lit/ds/symlink/lmd18201.pdf
Can on your own, company like www.cbas-usa.inc
in CA can do the assembly for you with pick & place machine for parts placement & reflow soldering.
You drop ship all parts & boards, they send back assembled cards via your Fedex account (easy to create one, fedex bills your CC when the account is used).
Are you familiar with eagle PCB software from cadsoftusa.com?
If not, I could design this card for you very quickly.
Pretty much add ardiuno circuit to this design and find a big old heatsink for it.http://www.dipmicro.com/store/L298N-MOD