The kosher butchery firm, Kelman's, added them to their non-meat range in 2006 but, although MySupermarket.co.uk (which is usually a highly reliable source of information) recognises the product name, there are no current stockists shown. Further, the Kelman's website seems to no longer exist and the domain name is no longer registered, which tends to suggest that they've ceased trading.
MySupermarket.co,uk isn't finding any similar canned products but these
https://img.mysupermarket.co.uk/Live/Products_1000/88/051588.jpg?v=20170912155508
are shown as available to order from Ocado for £3.79 but as currently out of stock in Sainsbury's, Tesco and Waitrose. However, if they're of interest to you, it might be worth keeping an eye out for them in those three stores.
Alternatively you could try making your own:
http://family-friends-food.com/chopped-fried-gefilte-fish-fishballs/