Bill Mollison has a really fantastic speech on this subject called "Funding the Revolution". Which can be found here: http://permacultureideas.blogspot.com/2010/07/free-audiobook-bill-mollisons-funding.html?m=1
He offers some great ideas for building systems to make money without compromising on the ethics of Permaculture.
With that said there are things I would buy, like land, but as far as strictly investing in I would focus on companies, products, and ideas that seem too far out to be plausible right now. The biggest realization I've had through the years of studying Permaculture is that there is a lack of design and forethought in almost everything. I'd invest in things that are trying to design solutions to problems we haven't run into yet.
As an example: Our civilization is going to run out of fossil fuels and as of right now the majority of alternatives to fossil fuels rely on fossil fuels for production. We can use the remaining fossil fuels to establish renewable infrastructure, but then what? I'd be willing to give money to anyone(assuming I had it) who was trying to solve the problem of producing future energy infrastructure without the use of fossil fuels.