re: Where is all the Antimatter?
Matter and anti-matter were created at the same time after the the big bang as universe expanded and cooled. They should have been created in equal portions, and subsequently annihilated. But, for some unknown reason, matter was preferentially created. I have read speculation that there may be great stores of anti-matter in intergalactic space but I've not seen any proof. You would think that if there were regions of anti-matter gas, you would be able to see the results as it interacts with matter.
Dave M