Turbo Scamp
Another member here, 67gtx, turned me onto a company in Florida called Blue Moon that makes a cap that fits perfectly. They've been backordered for months, but told me another company called British American Transfer, Inc. imports similar caps from England. This is a cap for airplanes. It will need to be turned down a hair on a lathe to fit my Scamp, and a vent provision will need to be rigged up.
Contact number for BAT, Inc. is 941-355-0005. Model #CAP2LF. Price was $209.30 plus shipping.