It is just about impossible to find, unfortunately. I bought some on eBay that turned out to be a bit of a darker yellow ("goldenrod") than what I was hoping. The best yellow boa yarn I've used is a nice bright yellow that is made by Mei Mei. Rick Z had sent me a skein of it several years ago. In the same sharing spirit he exhibited, I in turn have gifted quite a bit of it to others.

My "lifetime supply" may not actually last me that long, but I can still share.

There are a number of manufacturers that sell boa yarn...it surprises me the lack of availability of many of the colors we are interested in. In addition to the yellow, other colors of it that are worth using include black, white, various shades of gray/silver, and orange. Brown, purple, ...I've seen a lime/chartreuse color that my neighbors used in some crafts, but I haven't seen it sold anywhere. Strange, right?