I am working on a new startup and I have to validate it by getting the feedback of my potential customers, aspiring entrepreneurs.
Have you thought about social media (i.e. twitter?) I rely upon twitter for feedback on a regular basis. Another option is to create a targeted list of the 500 people/organizations you specifically want feedback from and send out via email, though as we all know the response rate on something like that is quite small. There are groups on LinkedIn, Facebook, Twitter etc as well that you could tap into.
Three ideas: 1) Post it to LinkedIn -- you will probably get more than 500 responses. 2) Work with your local Small Business Development Center (SBDC) -- In a "fish with there the fish are" sort of approach, you can expect SBDCs to have connections with many small business owners and entrepreneurs -- they offer free advisory services to such individuals and can put you in contact with them for your survey. 3) Check out www.1MillionCups.com. This is a weekly program held in more than 50 cities across the country -- each week, in each city, two entrepreneurs present their company (usually startups and young firms) overview in 6 minutes or less, followed by about 20 minutes of Q&A from the audience. This is another place to connect with a lot of entrepreneurs very quickly. Good luck!
We have over 50,000 mostly business followers on Twitter. If you want to broadcast out a message or a survey let me know.