PVC fittings.com is a good resource.
Offering the LOWEST ONLINE PRICES on PVC Fittings as well as Plumbing Supplies – Piping, Valves & More. We Stock Schedule 40, Schedule 80, CPVC & Metal Products.
www.pvcfittingsonline.com
A lot will depend on your storage tanks and their opening sizes, and the pump you will be using and its incoming and outgoing size.
For reference, the valves are called true union ball valves on their website.
If I were to do it over and knowing now what I do, one change I would make would be to have a valve and outlet immediately at the RODI water exit, so that I could dispense clean RODI.
In my current set up, I only have one water outlet (in the middle with the silicone hose) and it’s shared by saltwater and rodi, so I either need to run a lot of rodi through it to ensure all the salt residue has been expelled from the line, or there will always be some minor trace of salt in any RODI water sample I may wish to obtain. So I would have an outlet near the rodi that never has salt water going through.