Hi,
Although I cannot directly help you in finding an ideal upright piano, I was in a similar situation to you when I was trying to get my perfect E.Piano. A couple of Forum Members responded to a post I made, and after spending an evening tweaking what they had uploaded to these Forums I ended up with my all time favourite E.Piano sound. I made a point of giving them the credit as without their uploads (onto the Forum) I would have never ended up with my perfect E.Piano sound.
I have a Korg PA4X (£3,000) and previously a Yamaha Tyros 5 (£3,500). Neither have an E.Piano sound that comes close to the one on my PX5-S (in my honest opinion).
I fully intend to purchase the PX5-S replacement when it arrives (hopefully this month at NAMM), but if I cannot get the same E.Piano sound from it then my PX5-S won't be going anywhere !!
Best of luck, hopefully someone will point you in the right direction on the downloads section.
Chris
p.s. have a look at Dave Weiser's piano sounds, maybe one of those might fit the bill (for a small amount).