Your local Evinrude parts supplier could probably help, as the Johnson parts on those small engines are most often shared with Evinrude.
I've got a similar aged 5hp Johnson (a Belgium-made one though, currently on one of the boats so I don't have the serial number to hand, but can check tomorrow), and Wills Marine in Devon supplied most of the parts for it's rebuild at a good price a number of year ago. I forget where the carb kit came for that engine as I don't think that particular bit was Wills Marine, I'll have a search and see if I can find any details - I suspect it was one of the usual UK suppliers on Ebay (definitely not knowingly from China). Most of my recent small outboard gaskets have come from SSI Marine, and seem to be Mexican manufactured, "RecMar" I think was the brand label. I haven't yet had any issues with them, and have various of their gaskets now in a Johnson 5hp, Johnson 9.9hp (a complete set, as the whole powerhead came off earlier this year to clean out the water passages) and Mariner 30hp.
Wherever the 5hp carb kit was from, it was fitted probably 10 years ago now, and still works perfectly! I just put one of the SSI Marine "RecMar" carb kits into my Johnson 9.9hp today, and will hopefully take it for a test tomorrow.