Actually, find a good designer in your own country and at the same time shop around in china for a chip factory with some basic specs of manufacturing requirements from the designer, then get the final design and pump out the prototypes. the problem with ASIC is that to get the best grade of power efficient to hash cracking ratio you need to use more and more complex techniques in that process which makes it harder to just 'do it yourself'. On the other hand, if you look at things like the Raspberry Pie boards, they wanted to originally manufacture in the UK but couldn't because ultimately in VAT it cost more to import each component then have them sent to china and then imported as a whole, they some how got around this later on but I guess it was only due to price drops in demand that made it more feasible.

So ultimately, you could come up with an 'open source' design but chances are the design wouldn't matter if it was open source as it's access to manufacturing and distribution is the difficult bit.