I had this laser disc years ago and sold it thinking it was a slam dunk that the extended cut would be released on dvd. The LD is damn near impossible to find on eBay, I've been watching for a couple years now. It's on my list; too, years ago I converted my LD library to DVD and I really wish that I had this one still when I was doing all that.
I just re-checked eBay and there's one up there, first one I've ever seen. Bid is at $10 right now if you want it badly enough. http://www.ebay.com/itm/Laserdisc-DEAD-POETS-SOCIETY-Robin-Williams-NOT-Rated-Color-142-Minutes-A113-/221176283525?pt=US_Laserdisc&hash=item337f224185