I've heard of reading about a Casio EP-20 that there was an integrated ROM Pack data chip from an unreleased "RO-267: Music from The Muppets" ROM Pack of 4 songs. Perhaps I or someone have to make one so all I/you need is to get a Casio EP-20, desolder the OKI MS268V-57 ROM data chip from the EP-20 and put it into an available opened-up ROM Pack (I would go for replacing World Songs, make sure that ROM uses the OKI chip) by desoldering the chip from the board of the opened-up ROM pack then placing and soldering in the OKI chip into the board. And there you go, a homemade Muppets Music ROM pack for use on other Casio ROM Pack compatible (e.g. PT-380, SK-8) keyboards!
Well that nobody has done that previously, I just wrote it down so people would notice how to do this stuff.