Eric,
I've provided formal written appraisals for firearm collections here where I am. This is usually done for an estate. A hands on is best, but a number of guys here would be "qualified" to give one, but if Bruce Karem or Mike Steves would do it, as book authors, that's very good. There is an appraisal fee which can range from $100 to whatever depending on the size of the collection. I do estate work and you want whatever it is to pass judicial muster. Some local gunshops will have an "expert" who will do it. These days it is more simple as it would involve looking at realized auction prices and sold listings.
Regards,
HB