Is this an older Hopkins or BWM or a newer style like what Ryonet is selling? Chris at BWM still has individual parts for the older Hopkins international presses. When I talked to him a few months ago, he said that the older styles can be retrofitted to the newer knobs as long as the main casting is there. If the main casting is broken, a new head would have to be purchased. I have an older 6/4 with wrenchless mircos and it looks like the newer style print heads Hopkins presses at Ryonet have are the same as what I have on mine. If that's what you're looking for, they are around $175 per head. I think BWM sells them for around $700-$1000 per head. Otherwise, each piece can be ordered separately through BWM.
Here's a link to the print head parts at BWM
http://www.bwmhopkins.com/customer-service/parts
Hope this helps!
Here's a link to the print head parts at BWM
http://www.bwmhopkins.com/customer-service/parts
Hope this helps!