Hi,
So, the best way to go infrasonic is custom DIY. There's not really a commercial market for this. And the real key is to design the sub enclosure and port it and actually tune the port to 8hz or whatever you're wanting to achieve. Buying a sub that is tuned to 14hz, 15hz, 16hz, 17hz, 18hz, etc, with its port is just going to not do 8~10hz without a melt down. So you have to build it and tune the port to 8~10hz yourself, or have someone do it for you and have someone mill/cnc the parts unless you're handy. Then work on picking the appropriate driver(s) (though should have been part of the box build and calcs). Powering it is the easier part.
Very best,