Hinge shoe
The piece you have here is the track slider from the window hinge. This isn't something sold separately, so you'll need to replace the entire mechanism.
I'm happy to recommend a replacement but I'll need to see a photo of the hinge. I'll also need to know the length of the track installed to the window sill.
Please let me know if you have any questions.
You'll need either the 36-048 or the 36-004-10 (stainless steel) 2-Bar Hinge Set to replace your existing hinges. To determine which of these might be the best replacement, carefully look over the specifications and compare them.
You'll need to replace both hinges on the window to ensure they are a match.