More Words, Deeper Hole

One theory of dark matter I've seen holds that antimatter was preferentially sequestered into droplets of unconfined antiquark matter at the QCD phase transition (thereby also explaining the apparent prevalence of matter in the universe without requiring total baryon number to be nonzero.) In this theory, there could be lumps of ultradense antimatter (with mass in the range of tons) sailing through the solar system all the time.

One could imagine these being detected somehow, tracked down, be given an electric charge, then towed back to Earth orbit to be used as fuel in annihilation reactors. Even at nuclear density, they would produce huge amounts of energy immersed in a gas of normal matter at reasonable pressures.