As a first step, contact the Arkansas Headwaters Recreation Area people (The River Rangers). They may have some info on who owns your paperwork, and may be able to assist you in some way. Also, try the Colorado River Outfitters Association, they may have some info.
Speaking from experience, I have never had to provide my original rookie year training log that demonstrated my 50 miles or hours or whatever, nor have I had to produce any documentation that shows I was "Class IV Certified". I have had to provide my own personal river logs, and this is pretty much a matter of course all over the country. This is the log that YOU, AS A PROFESSIONAL RIVER GUIDE, should keep yourself. This is your resume, your qualifications, your means of proving yourself legit.
When I was guiding, I would scratch down in a notebook the river section, my load, the level, if I had any swimmers, and my tip. This was mine to keep. I would do it when I filled out my time sheet everyday. From this I would recopy this without the extra stuff, just the section and mileage onto a another log that I would copy and give to the company, along with my CPR certs.
If you don't have that daily log, go back and reconstruct your seasons with a calendar handy. This will give you a pretty good rendition of your river log. Be conservative, i.e. don't inflate your mileage, and you shouldn't have any problems.