The best thing to do in this scenario is to establish methods for gaining parent information from the parents directly. This is called permission marketing. While it may seem a pain at first, you may find that this will actually be a good thing. You will have to establish better communication with the school families, and that communication will lead the way more involvement, etc.
Setting up a table and sending sheets home with the students are both valid ways to do this. You may want to consider some kind of incentive for parents to give you their information. Can you get a local store to donate a coupon? Or maybe just list the benefits of signing up. They might be a monthly newsletter that talks about what is happening at the school, a year end report on what the parent group accomplished, invitations to special events, etc. If people know they are getting something back for sharing their contact info, they are more likely to share.
Be sure to collect all info, including phone, email, Facebook id, etc.
I'm in Northern Nevada and we are using a technology called
the groupery
to manage our PTO directories and membership through email groups. It's really easy to use and is more than just a broadcast tool, you can collaborate and have many sub groups within the tool. So for example, right now I'm leading a fundraiser for a carnival and we are using this to communicate quickly about who has solicted whom, what we have gotten donated, etc. They also have great programs that allow you to setup flyers, online calendars and use technology to raise money on-line through GoLocal advertisements. It is exciting because we will reach people that don't normally have time to come to the school through email as a new means to communicate. You can limit advertising to zero or you can use local merchants to advertise and your PTO earns part of the proceeds which I'm getting ready to implement this Fall.
We may be using it in 2010 to build out membership directories that we click one button to print them and sell them as a fundraiser.
We always set up a table at Back to School Night and have people sign up then. Also we send the forms home with the kids, and if the parents chose to sign up then, they will be members!
if the parents voluntary gives it to you as "a friend" maybe that would be a way around it.
Could the school send the forms out for you?
Another way might be to setup a cheap website with messages on it for parents to check and have downloads of the forms.
This is a tuff one but if you find a way that works please post it here incase, we have this problem in the future.
Good Luck!