Is anyone still making slide copy film? Can you get reasonable results from ektachrome or similar? Otherwise I could scan them, but there is no fun in that.
It is worth remembering that there can be quite a bit of batch to batch variation in colour balance with dupe films so either get a bulk roll or make sure that all rolls are the same batch.
Ektachrome SE dupe or Fuji CDU-II are the rare, but tasked to the job products.
Other films can be used, but work best with flashing to control highlight contrast, as I recall.
I will soon be putting a big post on my current interneg film calibration efforts.
If you can no longer get slide copying film, I used to find that I got better results if I copied them with a different slide film than the one they were shot on, and as low a contrast one as possible.