Customs workers at the Port of Suez discovered they were expected to clear seven tons of tear gas arriving from the United States, and were questioned when they refused. they also have documents showing that it is the first of three shipments totaling 21 tons arriving from the US. More on the story here. CS gas, which in the US is supposed to be limited to military use, has been extensively used against the demonstrators in Tahrir. Some reports say even more restricted types of gas have been used as well, possibly CR, which is labeled a "combat class chemical weapon."
The US is not the only seller, though the "Made in USA" canisters have been much photographed. China has also supplied, and many of the canisters contain no country of manufacture, so the demonstrators have set up a website, Tear Gas Identification, displaying various canisters and asking readers to help in identifying sources. I don't think all of these are actually gas canisters, but if you worry about who's supplying the authorities in this case and can help in identification, you might want to take a look.