Not sure of your ages, but here is what I have on my shelves:
If You Traveled in a Covered Wagon, Ellen Levine (in print)
How I Survived the Oregon Trail: The Journal of Jesse Adams, Laura Wilson (in print)
Oregon at Last, A. Rutgers van der Loeff
On the Oregon Trail, Wilma Pitchford Hayes
Children of the Covered Wagon, Mary Jane Carr
On to Oregon, Honore Morrow
Oregon Trail, Francis Parkman and Samuel Morision (older kids probably)