Cane sugar is regular tablesugar that you buy in the grocery store. You should not use this, though. It's sucrose. I know you said you know what is is, but you also just asked where to buy it.
Dextrose is corn sugar also called priming sugar. You buy in at the LHBS. It's about $1/pound. You use 4 ounces per batch. You can keep it indefinitely in a ziploc bag or canister.
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