Normally a good butcher should be able to provide it for you. Not sure if it's similar but you can buy tins of Goose fat from likes of Sainsbury's and Asda. I would imagine it's the same sort of thing.
Somerfield also stock goose fat its around £1:50 for 160 grms, or you could always buy a smallish frozen duck for around £3:50 plenty for two, and collect loads of fat for free.
