There's a jack repair expert over on the Garage Journal board who goes by the screen name of Hiball. He was selling seal kits but I think at this time he's just recommending sources to buy parts. Besides him there are a number of other discussions about rebuilding Hein-Werner and Blackhawk jacks and where to get parts, I'd go over there, join up and ask (and also search, that forum uses the same format as this one so everything looks and works the same.) I did find one source that was mentioned:
https://www.blackhawkparts.com/index.html Also, try using Google Maps - use the 'find nearby' feature to look for hydraulic repair in your area, I found several places nearby to Latrobe that work on and sell parts for hydraulic rams.