The odds of you finding that pump assembly at a price you'd want to pay, are not very good. Given enough time, you might find a cheap SJ-2 for parts. I have two SJ-2 jacks, one is Blackhawk branded, the other Sears branded. One is my user, the other a parts jack, because the main cylinder is corroded beyond a quick rebuild. I'm not ready to sell off parts from it though, as I may need them someday.
The rebuild kit I purchased had issues as well - I found that the pump cup was allowing the jack to ingest air, and I was constantly bleeding it. It had a very small "notch" at its perimeter, and I noticed that every picture of one I could find on the internet, had that same notch as well, maybe from where they were separated when taken out of the mold. And at $28 for a replacement (just the cup), I wasn't going to buy another one. I ended up making a new piston, but of a different design, so as to use readily available orings and backups (pics below). Using the original cylinder, my choice of oring size was a compromise, and I had to switch to ATF to get the jack to perform in cold weather.
The scoring on the piston is inconsequential. If the scoring in the cylinder is the kind that you can see and not feel, I wouldn't worry about it. If you can feel it, you may be able to hone it out:
https://www.zoro.com/flex-hone-tool-flex-hone-18mm-0709-600-grit-sil-bc18m600/i/G9931945/. Somewhere between 320 and 600 grit might do it. You'll need to measure the ID, but mine is around 0.688, so 18mm on the Flex Hone.
The last pic shows the cup that came in the kit.
