You may have more than you think you have. The more names, dates, and places you know about, the more productive your future searches will be. The following suggestions are not meant to exhaust the field of possibilities. They represent either specific things you can do, or ideas of the kinds of resources that may be available for your area of interest. This is by far the most comprehensive list of overland trail documents so far compiled.
Mattes gives a brief description of each journal, and where it is archived.
The indexes give lots of information on years of travel and travelers identified. For example, the Oregon Historical Society library in Portland has a card file with thousands of names of pioneers. Some contain just a traveler's name. Others have extensive information on the person and their family. The Genealogical Forum of Oregon library in Portland has a less comprehensive, but similar file.