i want to install ball valve on my raw water hose, in between inner transom plate and water pump. Already have a T in it to plug the garden hose to run engines on trailer, but i want to be able to shut the water and stop it from going out back in the drive. Very easy to find the ball valve locally, but no one can help me having the right size adaptor to be able to connect the hose back on each side of the ball valve! Can i find this easily online? I checked cp performance website and i was not succesfull finding it...
any leads to this simple add on ball valve ?

Buy a 1" NPT female thread ball valve and screw in whatever size hose barb to NPT fittings correspond
to your hose diameter.

Have you been flushing through the Tee and letting water run back to the drives previously?

The issue I would be concerned with is the actual ID of the valve. While the fittings can be the size needed, but the actual ball hole is smaller. Need to find brass or stainless fittings because they are made with a thinner wall. I would suggest starting with fittings like Hardin marine SS 1.25 ID. Then may need bushings to go to 1.5 ID so the hole will not cause a restriction

Pex valves are great for these issues but would not suggest using it in your app because they don't have ends which are designed to be held by hose clamp.

A full flow valve will have the same ID as the barb fittings and hose.

OK, guess its finding the full flow ones

eBay is your best bet.
I found USA made full flow stainless 1.25" valves for around 35 bucks

Can't you just buy a Parker Hannifin ball valve? McMaster Carr.....

Full port valve

sure, you can. I bet you're gonna pay a good bit for it though.