wellaem
keep your eyes open at the local dump/recycle center. Many charcoal grills have those, and are free for the taking

oldman49_2000
You will be able to find cast iron grates in various sizes from a reputable fire place store supplier.

Tommy C
type in cast iron cookin grates on line

Eagles Fly
If you know of a welder in your area and if he's willing, he could make you what you need. We had this done for our pit. Most welders who have been around for years, may have something lying around that the welder might sell you. Ask if he could make one for you. He probably will. That's one of the reasons he's in the business. We've had him do a few things for us. Sounds like that's the way you're going to get what you're looking for. We haven't had a conventional grill in years. Gave up on them. Seems you're always having to by parts. We do all outdoor cooking over our pit. You can also get a try pod for cooking over your pit. I think food tastes better, cooked over an open fire pit. Welder could also make tools you may want to have. Good Luck