Attend conferences and ask to present or host a workshop. Many events are happy to have us as presenters and will typically give us booths and advertising for free. Make sure you have local language hand-outs (here are some examples).
Search for non-profit, charity and governmental organizations that work with people with upper limb differences. Google and Facebook are great tools for finding these groups.
Post photos and videos of your test hand to Google+ so that others can see your work and contact you. Consider spending a little money to promote your posts to a wide local audience.