I do collect romantic concerto scores, but i hate & have to admit that i have not got this. I have been advised by a fellow collector that this is unpublished and the manuscript is in "private hands".
I did spend a few hours searching libraries, but came up with zilch, so this is quite possibly the case.
Writing to the conductor or the pianist that recorded it could yield results. This has worked a couple of times for me in the past.
Good luck, and if you find it, can i please have a copy.
Thal