The short answer, at least in this country, is that sultana raisins are golden raisins and you can find them everywhere. But we seldom go for the short answer, do we?
There appears to be a good deal of imprecision in the raisin arena. There are three common names for raisins in the English-speaking world - sultanas, currants, and raisins. Of course, sutanas and currants are raisins - that is, dried grapes - and among purists the word raisin is supposed to be used for any raisin that is not a sultana or a currant. But that doesn't always happen.
Currants are tiny raisins from the zante grape, and are supposed to have been first grown on the island of Corinth in Greece. Generally, currants are more tart than other raisins.
Sultana raisins were originally the product of the Sultana grape, which grew in Turkey. But in this country, 95% of the grapes used for raisin production are the Thompson Seedless variety, which dry and darken in the sunlight, producing the common raisin. The same variety of grape, however, treated with sulphur dioxide and heated artificially stays lighter, moister, and plumper, and these are what are sold here as golden raisins or sultanas. Theoretically, sultanas are sweeter and less acid than other raisins.