I'm also looking to purchase a UL4 steel string if anyone has one they're thinking about selling or knows where one can be found. In Feb 2019, HMS had two in stock (ebony/spruce & mango) and they both sold. According to HMS support, Pono UL4 steel strings are still being produced, and they "think" they should be getting more in stock this spring, but they don't know the exact date/models at this time.
If anyone is thinking about selling theirs, please let me know! My preference is for a spruce or cedar top, but I'm not opposed to mahogany or koa, either.
Thanks all
PP