I have a 3700gph I would consider selling
And I have a HUGE pump that looks like it came off a swimming pool, lol. I got it from a friend with no real info. But its crazy big.
Aside from those, there is a hydroponics store called "Indoor Gardens" on the east side that sells pumps. I got a 1000gph magnetic driven submersible pump over a year ago for less than $80 and it has worked great for me. I know they had bigger pumps, but I didn't check the brands or prices.
Hope that helps ?!?!