Here's a review of Oregon Trail for the Apple ][. They include a pair of links to a ROM for it as well as an emulator.

I'll have to be honest -- I had to read the article because without it I'd have no idea what you do beyond the first half of the game. From grade five on, I was never able to find a disk in the school that had a working B-side of Oregon Trail.

Oregon Trail for Apple ][ Emulator