I can help you get visas, and I work with lots of founders on that sort of thing.
Check out these folks as an option for getting your sponsor: http://www.internationalexchangecenter.org/
However, most startups won't be certified as a J-1 sponsor, so I can help there through working with USCIS, make sure the process works out.
Have you checked to make sure that J-1 won't require you to spend two years physically in the Czech Republic before applying for another visa? http://j1visa.state.gov/participants/common-questions/ (check tax and immigration requirements)
I have an email in my profile if you want to talk more.