You can get them from Amazon in the US here is the link
Johnson Pump Cartridge Bilge Pump

Depending on the size of your ROV, you can choose to have more trust, but that will require more battery power. I have tested the 500 gph/1900 lph Johnson Pumps to 30m and never had any issues. If you have problems in deeper water you can drill a small hole in the side of the cartage and fill it with oil, just make sure you get all the air out the of the cartage. Seal it up and you should be good for at least 60m.

Regards

CALLA (Gansbaai South Africa)

PVC:
Body – 4 in sch 40
Body front and rear – I think they are called knockouts. Get the ones that have the bolt holes drilled in them. The back as a cover that bolts on with stainless steel bolts. The front has the lens which is 1/4 plexiglass. That is bolted, epoxied and is not removable. You can get the epoxy from Lowes plumping department. That seems to work good, or the plastic epoxy from Home Depot. That seems to last longer but is not as strong.

Floatation – 1 in sch 40

Connections – all 1/2 in sch 40

Wire harness – 1 in compression fitting, this will allow you to unplug the unit or change the wire harness to meet depth needs. Longer the harness the more power you need.

Motor housing – I think they are 1 1/2 to 2 in reducers
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Motors:
I used 500 gph attwood bilge pumps. These are the same pump cartridge that I used.
Attwood Cartridge Repl. Tsunami T500

They are a little different shape but should work just the same. I have tested my pumps to 50 ft without any issue. If you want to go deeper you drill a hole in the body and fill it with oil. There are four pumps, two up/down and two left/right. I used brass tubing to connect the props to the pump shaft.

Props:
I have a couple of different props. You can use RC plane pusher prop, they are big, so you will need to cut them down. I also found boat props that fit/work much better (shown in pic). I found them on ebay in Hong Kong. It took 5 weeks to get them. So if you go that route I would order them now and get a few extra. I lost one prop in 40 ft and had to change to the pusher props to go find the lost prop. That took all day…

Wiring:
This is a big issue. I use cat-5 network cable and double them up. I need 4 pairs to drive the motors. Each pair consist will use 4 wires I solder one of each colors from each cable. So brown to brown, blue to blue and so on. Then pair the colors up brown negative and brown/white positive. I found that a single cable losses to much power due to the thin wire. Also add little pieces of foam to make the cable neutral buoyant so it does not drag as much on the ROV.

Camera:
I have a high resolution security camera that has auto adjust focus and light. But what ever camera you choose built the ROV around it as tight as possible.

I think that should get you started if I missed anything let me know.
Good Luck and keep me posted on your progress.