It doesnt even cost you a dollar on ebay i think and its way cheaper to buy 2 8gb sandisk/kingston sdhc and combine them to a 16GB one. Heck go for a 32GB. Is still cheaper! Im currently using 8GB combined with 16GB. Took the 8GB from my DS and replaced it with a 4GB xD.
EDIT: The largest memory stick from sony is actually 2 TB which was done together with SanDisk. And they cost ridicously high and i believe isn't sold on normal shops.
They are also from the XC series. Not the Pro series which ended at only 32GB
Heres a picture
And proof of a 32GB sold in a Norwegian netshop at Stavanger or something.