Check out "Alliance-Express", who specializes in plugs and caps. Their
catalog has over 100 pages of various plugs and caps- internal, external,
threaded, slip-on, etc. Spoke with a rep on the phone and they will sell to
individuals. The URL is Alliance-express.com, and the phone is
1-800-489-2636. They have a number of options on material, size and color.
My first thought is to go with a vinyl (pvc) product in Black (more UV
resistant). Check out the "dip moulded vinyl products" section. Good luck
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