Most people use a washer pump for an automobile wind screen.
They can be found cheap at the auto wrecking yards, and there are
cheap replacement pumps availabe.
One of the best ones I have seen was a volvo gear pump. The
gentleman said he was able to replace the motor with a higher rpm one, and
it really puts out the water. And gear pumps are self priming.
I manufactured my own for my fire boat from an old pump housing a friend found.
It has its own issues, but pumps about 350 gph (1324 Lph). There is a small fresh
water pump from a company here, in the US, called Grainger. It moves that volume on 12v.
http://www.grainger.com/Grainger/items/1P811
It has to be below the water line , as it is not self priming. Most pumps are that way, but
that volvo gear pump, if you can find one could be anywhere.