Give the parts guys here on the site a try. They have a LOT of parts, and can get ones they do not have.
It's often faster to call them than to locate parts on the webpages. Call them at 877-932-7245, they are open 9 to 3:30 Pacific time.
Bomar has many replacement parts for hatches, though they can be pricey. I elected to find my hatch arms at a local marine salvage yard, but Bomar would have been happy to sell them to me. Give the Bomar parts department a call at 603-826-5791. I've talked to 2 different folks, and both were very helpful. I called them from the boat, and they asked a series of very specific questions, including measurements, to help me identify the multiple parts I needed, including arms. Good luck.