I first saw ExpessCard SSDs on the shelves back in January, and since that was an airport Dixons (CurrysDigitalwhatever) I can safely bet they've been around a few months before then ;)

Lexar seems to have a nice range, and Sandisk do too; if you can find them anywhere on their website...

many expresscards simply use usb (expresscard is always pcie x1 + usb), so most expresscard "ssds" i've seen are just repackaged usb sticks