I really wish people would clarify what they mean by "free market" -- whether they mean
unregulated (a politician's free market) or
competitive (an economist's free market). If you are saying that there are no examples of monopolies in competitive markets, that's because it would be a contradiction in terms. If you're saying that all monopolies are created and enforced by governments, then that's just flat-out false. Pepsi and Coke dominate the industry of selling pop due to branding; the only "government enforcement" of their domination is that you can't brand your own pop so that it would be easily confused with Coke. Same with Microsoft -- the US government never threatened to jail you if you don't run Windows, but Windows had a monopoly on the desktop market for a while and it's only recently begun to show cracks.
I would go so far as to say: governments themselves are "free-market monopolies" in this sense. That is, there is no binding unilateral authority which solves intergovernmental disputes, and each government instead has to negotiate with other governments in an open and unregulated forum where even backstabbing and flagrant contract violations are permitted. If governments are monopolies on power, then the market of power is surely not a well-regulated one.