If your designs are to be open sourced and shared with the community, then why are you being so secretive? Just share them here. There are many OSH developers with good 3D printers and laser cutters, etc., not to mention those services are readily available so you don' t need your own machine.
If your ideas have "legs" people will be happy to jump onboard and help out.
If you are really proposing open-source, then you can get all the help you need online and the need for sponsorship declines dramatically, as does the need to get companies involved. Businesses join things that can make them money or save money. Show them that your plans can do that and you'll find interest.