Try targeted advertising in the local community-based magazines.
I live in a relatively conservative region in Los Angeles, receive a local magazine chock-full of home-related services and local issues / news. IRC, I've seen an ad in it for a local instructor, who runs some classes at the local ranges and hotel conference room. He's also apparently done well enough to run commercials on our local cable network (running on major channels, not tucked out of sight on the public-access channels)
His name is Richard Stefani -
http://www.sdfirearms.com/default.asp
Despite Los Angeles being roughly half conservative (based on Presidential and Governor election results), and being stuffed with guns, the gun owners here are very much 'under the table'. Firearm businesses have long been harassed by City and county government. Of the dozen firearms businesses I used to patronize in the San Fernando Valley / northern half of Los Angeles, I don't think there are three of them still operating / worth a damn. And don't even get me started on what K- and Walmart have done under California's pressures.
I'm in Santa Clarita Valley and there is not a single firearm store here - a conservative region with something around 200,000+ people and still growing steadily, yet the only such business up here closed their doors a couple years ago.
We are under siege here, and gun owners general behaviour reflects it.
There is the Oak Tree Gun Club south of us in the Newhall pass, which does have a nice gunstore attached to it, but it is not convenient at all. Other than it, I have to drive nearly 30mi into either Glendal or Reseda to reach a place for anything besides cheap ammo at Walmart.
I've been contemplating such a Training / Traininer course myself, I routinely train acquaintances and I think I have enough of a word-of-mouth network to kick-start such a business
as a sideline. It just doesn't seem to be a business with many potential clients, here in L.A.
Compounded by the block on CCW, as well. In fact, Stefani's business seems more tailored to the 'FL CCW by Mail' seekers.