The Weldon Pump Co. provides curves of their pumps-- flow rate vs pressure at various input voltages. They are really expensive, though.
I have a DC pump made by Weldon that was made for a winterization kit for a 30kW diesel generator that may work for you. There are only military part numbers on it so I've never been able to track those numbers to a pump that has published flow curves.
The only catch is that it is 24VDC, not 12VDC. The pump is also rated as 3.3 amps. If you can use it, let me know, Bill.
Regards, Neil Tucson, AZ