Hi Anthony,
I wouldn't dismiss the Asian ones, at least for hobby use. Here in the UK, I have had a scissor knurler made by Soba (Indian, I think) and it is still going strong with its original diamond knurling wheels. It has been used mainly on mild steel.
You asked about dimensions. 0.75" diameter seems the norm over here. The Soba ones are 0.370" wide, and a set of wheels from a different source are 0.366". The Soba ones have about 5 thou axial play on their shafts, but I don't think that matters too much - in use, they soon settle down as they begin to bite the workpiece.
Andy