A friend in aerospace made me one, out of medical grade plastic stuff, for my small window aisin, looks better than the original, it fit so well I could have ran it with out the screws or plate.. Also looking at the old small window and then a latter fj60 carb, the sight glass looks almost the same....but they are probably not
1 barrel large window....seems to be some of those out there.
After I had the small window made, I was going thru my stash of parts and found a new OEM in the bag..
If it's just the flat, round one, you can cut glass or acrylic of the proper thickness and use that. New O rings come in rebuild kits. Or, you can send the carb off to one of the rebuild gurus on MUD and they'll replace it as part of the rebuild.