I saw this article about a Bristol mum having some issues trying to find formula. Looks like the Tesco Express nearby in Bath Road in Bristol had the product.
www.bristolworld.com/news/aptamil-baby-milk-formula-mothers-concern-over-shortage-after-trips-to-waitrose-asda-and-tesco-supermarkets-3478162
The article says if people are having difficulty to get hold of the their usual infant formula milk they can get in touch with out careline and social teams who can try and help locate products for them, either on retailer websites or directly on the Aptamil website. Hope this info helps someone!