Welcome to AC, peggy. Once you have decided on the region you wish to travel, try calling some of the bike shops along your route. They may be able to hook you up with trekking and travel support outifits. There are many. You can spend a few hours searching the Interwebs for support companies, too. They're out there.
You're paying for their time and gas and lodging, not cheap. Some outfits provide mechanical, meal or emergency support along the route; others just move your gear. Be sure you know what you're buying.
Sections of the Lewis and Clark route can be done easily by carrying your own modest luggage. Minimalist credit card travel is fun and easy; you need very little to be comfortable and warm and dry if you're taking your time and know you will do some laundry each evening.
Hope you enjoy your trip. The L&C route through Idaho and Oregon is spectacularly great!