After months of relentless searches online and so many unanswered requests, there's finally one typewriter ribbon manufacturer in Canton, China, agreed to sell me black-blue ribbons! The best thing is, it costs only RMB14, approximately US$2, a piece, made of nylon and 8 meters long!
Months ago, I tried their violet ribbons, top quality!
They told me that, if the size of order is big enough , they can do all-yellow ribbons too. Once a Singaporean client bought from them a big order of four-parallel-color ribbons: red, yellow,blue and black, so that each and all typewritten characters have four colors.
Since I have no interest in yellow ribbons -- I have no idea of on what particular occasions do I need yellow ribbons. FYI, in China yellow flowers are for the dead--I'm trying to convince them to go with both dark green and brown colors just like the old times.
But they said ,to do that, they need to invest in developing formulae for the said colors, which in turn entails possible risks. So before that could happen, they need to be sure that the market big enough. I suggest them to list the products on eBay and try their luck.