You can buy "MPB" (minimum pilot bore) sprockets & bore/broach them to suit the application.
Or, buy pulley stock, cut it to the right width, bore/broach, & roll your own flanges.
There are also a number of shops that specialize in stock/custom timing pulleys.
I kinda thought QPD used the pulley stock approach.
But, I haven't seen one and can see how using an existing sprocket for the hub might be the most economical approach.
Like Ron says - this'd be a fun area to dabble in.
