Overflow bottle cap

I tried a few different caps from gas weed eaters and chain saws but didn't find one. Maybe check a wine or liquor jug?

There's a parts bike posted recently, or try eBay?

I hadn't thought about chain saws. I have checked brake fluid bottles, Margarita mix bottles, even odd soap and insulated sports water bottles. I know I can probably fing a new one but I am really trying to find and repurpose something since I have the actual overflows. They aren't pretty since one was the first attempt at heating one and reshaping it for the MCCT. It is ugly and leaked a bit until I used some high temp hot glue to seal it. Still ugly though. I actually should be able to find the caps that came with them years ago someplace. Hopefully. Thanks for the ideas.