I dont understand why it is so hard to obtain one it is 45 mm
Rob, you are learning that live steam products are made in small batches, and when they are gone, they are gone. It's not like plastic LGB locos that are made in the thousands.
The Ruby was originally produced at least 20 years ago, when Accucraft was just starting their business. They did produce 5 versions, one with a tender. But those have not been sold for many years. The basic Ruby soldiered on as an entry level loco, and they recently added the kit version.
This old thread asks the same question, and has photos of some options.
Ruby Progress