Need help finding rubber washer

Hello everyone! I have looked and looked, but I can not find a flat rubber washer with these dimensions: 4" ID and 4-1/2" OD. The inside diameter can differ slightly. I have a floor drain that I need to seal. I appreciate any help you can offer. This is driving me batty.

Simplest would be to just get a piece of rubber and cut out your own gasket. Six inch squares of rubber gasket material is commonly sold at hardware stores.

A drywall circle cutter, used for can lights, etc., will work if you don't have another tool.

Don't forget to do the outer circle first.