Issue is finding the blacktop that you can use without any issues. Here owners are very reluctant due to liability.
Smack...
I understand that locating pavement is a challenge.
Out here in the West, specifically the Lower Mainland(Vancouver) we are down to the use of one airport area of tarmac.
This area is booked every weekend by the various Racing clubs in town, UBCSCC, VCMC, BCCC, Porsche club, etc..
It is also used during the week for closed events for dealerships and Auto makers, BMW, Chrysler, etc.
The costs of these lots vary from $1200-$2500/day, depending whether you want a small area or to run a big course!
Back in the eighties, before Sunday shopping, we used to use shopping malls but that went away..
We then used a couple of the University parking lots on Sundays.. that ended when they realized they can, and should, use these 'schools' 7/365.
Liability issues are a real concern for the people controlling these lots.
As a group of competitors you may consider contacting an insurance agent to acquire liability insurance as a group.
Remember that this is not 'racing' and should be referred to as 'driver training' or 'skills improvement' exercises.
I can provide you with some basic rules on how to safely lay out a course if interested.
Some clubs usually run a Slalom School early in the Spring to introduce the hobby to new people.
No clocks allowed...just some driver training in a controlled environment.
When my sister bought her '04 Vette a few years ago I talked her into taking the Slalom School.
She learned a lot about what the car can do, but also improved her driving skills.
graham