[jyl]

In most industries, LinkedIn is a very effective way to reach people.

The more niche your business is, the less likely that a single agency or headhunter will have a candidate.

You might consider if the job can be split into two roles. You seem to be looking for 1) a sales/marketer, 2) a writer/editor, 3) an uber-geek in a rather obscure/unfashionable topic, 4) lives in or will relocate to your area, 5) not already happily employed. Draw the Venn diagram, that's a rather tiny intersection.

How many people with attributes 1 2 4 5 will have read that 80 linear feet of stuff, or can/will do so, in their spare time, in less than a decade? Do you plan to pay them for a year just to read full-time?