What is the brand on the fixture? Is this on the tub fixture (diverter to the shower)? I can find similar parts, but brand matters... And there may be a rubber gasket that is part of this.
If you know the brand, call the mfr. I've called Delta a number of times for my kitchen faucet to get new aerators and recently a new handle. Many carry a lifetime warranty.
What is the brand on the fixture? Is this on the tub fixture (diverter to the shower)? I can find similar parts, but brand matters... And there may be a rubber gasket that is part of this.