From Amazon
MasterClass KCMCHB56 30 cm Deep Cake Tin with PFOA Non Stick and Loose Bottom, 1 mm Carbon Steel, 12 Inch Large Square Pan , Grey
Dunelm
MasterClass Non Stick Deep Loose Base Cake Pan Square 32cm Grey
The Cake Decorating Company
12" / 30cm square non-stick loose base deep cake tin