Just bought our house, it was built in 1987 and after a month the cold water wouldn't turn on in the shower. A plumber came and pulled the valve and we saw that when it turns the "plunger" doesn't move in and out. Well, with a photo he wasn't able to ID what brand, the previous owner didn't know either. So, the home warranty doesn't cover "opening up a wall" and we're left with a desperate hope that we can find out what brand the valve is so we can replace it. If it helps, the house is a "custom home" so most appliances and such are all high end, my guess would be the same for the shower. I'm including a picture of the knobs too, in the hopes it triggers a memory of a brand.

 

Welcome to the forums.

There are hundreds of different plumbing stems. Without a manufacturer I would take that to a home improvement store where they have many on display and you could visually identify it. The site I use for online ID is in the link below but still not easy without a manufacturer.

Alfano Plumbing Parts | Compression Stems