I suggest you buy reproduction FI parts from John DeGregory or Paragon. Both of those are honest businesses who care about customer satisfaction.
There aren't many folks who sell original Rochester FI parts. Most of the professional rebuilders keep their spare parts for future use on customer units. I've been selling mine through eBay, including several high pressure gear pumps over the last few years. I've still got a pile of stuff to unload. However, since you've never bought anything from me in the past, I doubt you're interested in any of the NOS and used parts I have.
Jim Neuffer in NY advertises that he has a large stock of original FI parts. I've bought some beautiful plenum castings from him in the past. You may want to give him a call.
Chris Wickersham in CA sometimes sells original parts on eBay too. You might call him and see what he's got right now. He mostly works on vintage race units, but he sometimes has very nice stock parts left over.
The reproduction gear pump shaft offered in the Paragon catalog for about $35 will work fine. It is a few thousandths undersize compared to an original, but it is very smooth and seals well.