There are a lot of Ukulele factories in China, usually in Guangzhou, and whilst some of them make the famous brands that are distributed internationally, (and some don't respect copyright), they also produce other less famous brands that only get very limited distribution. These may be the factory "house" brands or may be a limited trial run and they never really went into production, (but then a trial run of 500 is more than some luthiers will ever make)?
I haven't found the information to be more specific, but some of these brands are as good as the famous ones made along side them so deserve some recognition. Some of the factories will have used more than one of the brand names on otherwise identical models of Ukulele and I am finding the more I look into it that some of these "manufacturers" are really only internet distributors who may be fronts for factories or may be small businesses with a shop on Amazon, Ali Baba or similar market places
Anyway here is what I have found.
Based Baiyun, Guangzhou and possibly founded in 2009, (from the Corona headstock logos?). They are a maker of all types of Guitar as well as a big catalogue of Soprano, Supersoprano, Concert and Tenor Ukuleles. There is very little information on the website but brand names I have seen them use include Corona, (on sale across South Korea and in South Korea at least they have some kind of deal with Hello Kitty for licenced Ukuleles - well the sound hole holographs look genuine from the photos I have seen?), and Taiyuan plus a Chinese Symbol that I can't replicate. They also appear to be an OEM for, if not own Pennate Guitars?
In 2014 they appear to have decided to focus on Ukuleles and had a big launch for their new top end brand Mauloa. They also introduced Uke Basses and Guitaleles in this range.