What you're referring to is Toronto magician, Jack Bateman's Rub-A-Dub-Dub, a rhymed cups and balls routine marketed by the renowned Buffalo magic dealer, Gene Gordon, in, I believe, the 1950s and later included in his 1980 book: Gene Gordon's Magical Legacy, published by David Ginn. Although probably fairly scarce now, that book might well be obtainable through the second-hand and antique magic book dealers. Finding the Gene Gordon original, with the printed routine and, if memory serves, felt discs supplied - in lieu of balls - in a printed envelope, is probably much more difficult and unlikely something you would need, anyway. This routine certainly could be doable by a beginner - although the rhyme might be a little much for today's audiences unless performed tongue-in-cheek or within an established character that this patter might suit. Good luck and hope you find it.