Some while ago, I had a machinist cut down a piece of 5" ID, thick-wall aluminum tubing into short sections to make up some tube end ring sets for 4.25" scope projects. [See these rings on a completed scope in the photo below] While looking for something else in packed away material, I discovered that I had one set of them left.
These aluminum rings are 1" in length, 1/8" thick, and will perfectly fit over the standard 5" OD tubing used by Edmund, A. Jaegers, and others over the years. They will also fit the 5" OD fiberglass tubes sold by Parks. [To my knowledge, niether Parks nor anyone else makes end rings for this size tube.] This set is not drilled for attaching hardware, but I can do this for you if needed.
Asking $17.50 for the set, plus postage.