Assuming yours is just like mine, you need to talk to Pelland Enterprises. The shower is called Majestic. The original manufacturer will NOT sell you parts and direct you to Pelland Enterprises. They're were very helpful in obtaining the hinge parts I needed.
Here's the link to their website. I suggest you use the shower document from the ACA website for reference when you speak to them. RV Parts and Motorhome Parts Online Outlet - RV Windows
Give me a PM if you need more direct assistance. I've spent WAY too many hours working on our shower but that does provide some experience.