you look up the feeder middle school results and contact those kids. they are already open to running. you just have to get them to do it for HS.
you obviously chase the TF kids who should be low hanging fruit.
you scout PE classes.
you ask existing athletes to double on sports for the whole season. soccer, hoops, but even others thinking outside the box.
or you talk to kids who have another sport about parachuting in for the state progression meet. like i won't make you do practices but can you come to meets. or the area championship. so you're not asking the full package.
all else fails, cattle call for any interested students. come try.
in terms of your related question, if you have basic numbers issues, only a crazy person handles their program in that scenario in a high mileage, high ambitions, harsh coaching manner.
you can carve up the group. if you have a few veteran kids with talent and fitness, you get the super serious workouts and train as group 1. ok, you are the out of shape noobs or players from other sports who don't show immediate genius, you're group 2, we'll do easier workouts and build you up.
honestly a lot of coaches on here sound like they just saddle up existing star kids. that's easy. and that encourages running the kids hard day 1 of practice. you have to actually make runners and build a program. you might want to work on a longer timeframe. my goal is to have you competitive by the end of the season. my goal is to have you good in 2-3 years. maybe they don't need 2 sets of strides plus 6 x 1 mile intervals to start their first ever practice.