Fruit stripes is a lovely name! In Tokyo there is an antique shop called Toritori which specializes vintage toys. The shop owner does Instagram. Please find her posts @nishiogi_toritori. I'm sure you would enjoy her posts and find something you would like.
I haven’t melted any of Seike’s marbles myself, so I don’t know the COE. For cat’s-eye base, makers typically used recycled cullet. The colored glass needs to be compatible with the base, so I’d guess they formulated the colors to suit whatever cullet was available at the time?
Satake started supplying glass to lampworkers in the early Showa era, but I haven’t come across any specific connection to marble makers—either transitionals or early machinemades. Have you heard of Kamitani? According to their records, they supplied colored glass to marble makers as early as the Taisho era. All the marble makers except Seike seem to use Kamitani colors. I once asked Kamitani about COE. They said they provide both soft and hard versions of each color so that marble makers could adjust for compatibility.
I had been a lampworker for almost 20 years. I loved Satake, but also used Moretti/Effetre and other glasses like North Star. You know Satake and that surprises me!