just a few ideas, I am sure some of them are already covered.
In terms of most trade magazines they are often produced by small teams who will work next week on a totally different trade magazines. Most of them will be looking for content to fill them up. If they can get someone else to do this it's all the better for them and the can get on with there real job of selling advertising space. It means that if you contact them, they will first try and sell you add space but if you can get past that and possibly get them to see how big your empire is and how a link to them from you could help them that may change there tone.
On a completely unrelated area I had big success with getting something out to police officers by placing a small add in their year book. This was in Ireland so it was more manageable (one book covered the whole country, in the US that may be totally unmanageable) maybe the fire service has an year book and a hugelkultur artical slanted to talk about the fire risk reduction benefits could have a knock on effect
Training packs, teach the teachers. I am not sure what the extension people you talk about are. I am guessing some kind of agr. advisers but they will get training somewhere. Find that person and develop training packs for them to use. I am sure there are other trainers you could target people with more local knowledge could come up with a list.
Don't get too focused on Hugelkultur. This weeks visit from Toby was a huge success. The forums and podcasts on all the different topics bring in lots of people, many of whom would never have clicked on a link that said hugelkulter, but once they are here they can't help but trip over hugelkultur. All general ways to build your empire also promote Hugelkultur. You are doing a great job, celebrate all the successes you are having on the broad range of topics rather then measure everything as falling short of this artbutory 50 million
Lastly I have to say I switch off when I see threads or podcasts from you about the whole light blub thing. Thats fine, it's your thing. But I am dissinclined to listen or read something that has moved up a level or so to ranting. I hope your focus on Hugelkulter doesn't reach that peek.