So a plan is evolving in my head...

I think I do want to do it "right". No not copper... I think I can
run the pex up behind the drywall at the the back of the closet and
have it come out of the wall, where it will transition to flexible
stainless tubing and interface with the softener. I've been
eyeballing it and I think it's somewhat doable. A hassle, sure, but
doable. So the PEX won't be visible.

I need a box that will fit into the drywall. It will be sort of like
a washing machine box (you know what I'm talking about) but it will
be a water softener box. It will accept two 1" ID PEX, turn 90 deg,
and then exit to two threaded 1" male connectors to which I can
connect the flexible stainless tubing.

Actually, I would just use a washing machine box, but these are
typically 1/2" ID.

Forced to, I may obtain a washing machine box and jury rig it. But
someone, please, please tell me I can buy the desired fixture off the
shelf.

In an ideal world the fixture in the box will also inlude an integral
on/off/bypass valve, but I can live without that.

Anyone know where I can obtain this? Thanks!