"Where can you buy vegemite in the U.S.?"
"Vegemite is not easy to find in the US, but you can still obtain it, especially if you live near a large city with an international population. I have not tried to find it near New York, but I am sure that I will if I try hard enough, and perhaps now I will. It is a Kraft product. On the other hand, in Australia apparently you see it everywhere you go.
If you are yearning for the flavor of the outback that badly you can order it online. Amazon calls it "Australia's Healthiest Export," but you will pay for that health. A 16 ounce jar of it sells for about 16 US dollars, but if you simply must have the taste of home, this is probably your easiest option. There is also an extensive selection of everything Australian here:
If you can settle for the UK version, Marmite might be easier to find in the US. But I am sure that I have just spoken sacrilege by comparing or equating the two.
Addendum: I looked on the Lower East Side of Manhattan, and quickly found 5 international food stores that carry it. So finding it is obviously very easy in a good-sized city. Then there is always the mail-order option, mentioned above."