As Jeff says, Yellowstone is now being made by a different distillery than 30 and 40 years ago. Sometimes when a label is purchased, the taste changes. I too recall Yellowstone from its heyday and it was in my top three or four bourbons of the day (the others were Maker's Mark, Old Fitzgerald, and Old-Grandad). It had a notable light fruity note, not lemonly, but more like strawberries or watermelon. It was very good and top of the line IMO. Some small stores, usually in the older parts of town, still carry the old bottlings but they are hard to find. I've heard there is some occasionally available in Washington, D.C.
In Louisville earlier this year, a small older store told me I missed the last one he had by a week, probably it was picked up by another enthusiast from this board or http://www.straightbourbon.com
(another fine bourbon resource). I felt better knowing another bourbon maven probably found it.
In terms of bourbons available today with that taste profile, to be honest, I can't think of any. You can try your hand at mingling two or three bourbons to try to get closer to the taste, again as Jeff suggested. You might try to find Virginia Gentleman 90 proof, the Fox as it is known informally. It bears some resemblances to the old Yellowstone and is about the same age (6 years old). If that doesn't do it, maybe combine that with Weller 107, 2:1. Even if it doesn't really come close, it will be very good, be assured.