Not know the name of the part

The piece you're looking for here is a slide for a larger hinge assembly. These are not sold separately by any company I know of, as they're riveted to the hinge assembly in the factory. You need a new hinge entirely.

We sell a ton of casement window hinges, which you can see here. Start by browsing through this selection. If you cant find your hinge, or if you aren't sure, please remove your original and show me a photo of it without obstruction.