Best way i found to find people to evaluate my business ideas was putting up cheap ads on internet. Started with Adwords five years ago.

Then you drive them to an landing page where you ask for the sale. But right before the purchase, you specify that the product is under development and will be shipped at an specific date. Thanks your "almost costumer" and collect his email for a future launch.

I think the internet is your best tool here, specially if you have some bucks to spend.