Used to be a common item for the large volume rebuilders like Jasper and AER.
Sealed Power had them at one time, as did Elgin, and Clevite. I think most were originally supplied by Manley - not the performance Manley, but his father's PA based business that has since had a couple owners and been sold away in pieces.
Not sure where you get them today, but I wager that an offshore supplier like Dandekar (India) or SA (China) has picked up the business. Cost means everything in that end of the trade.
