You could always make them yourself! It's very easy. Just the same as you would cook them with shortcrust but with puff pastry! Sainsbury's do sell them, I work there. You'll find them in the bakery section in clear packaging, possibly on some kind of multi-buy offer. I think there is 4 in a pack and they are quite large and circular but they do not come in little foil tins. Such a detailed reply for the humble mince pie ha ha xx