Ok here's an idea. the early or rather older model transmitters, correct me if i'm wrong had 5 watt outputs on 72 mhz. And another idea there are fm tranmitter kits on sale on the web and tv channels 2-6 are on the 72mhz band and have higher outputs with what i think is called a booster amp for the final stage. u might want to speak to a ham operator for tecnical advice here. hope these things help best i can do for now i was a tv technician before i retired . Everything has changed since then 20 yrs ago
http://www.hobbytron.com/R-LPA-1.html check this irl out??