They are sold through plumbing and pump supply houses. They are made by Ecowater and have the same valve and nonindustry standard clamp om tanks as a Kenmore, Whirlpool, mortonsalt.com, GE at Lowe's and Ecowater softeners except they have two separate tanks and the rest have the resin tank inside the salt tank; called a cabinet model.
They have a rotary disc valve and last about 2-5 years before they quit. You would do much better buying from an online dealer like me and installing it yourself or hiring a plumber to install it. I suggest a Clack WS-1 control valve. Depending on the size of the softener, you'd probably save $500-$1000.