I don’t provide the cake as it would be too complicated to meet everyone’s design needs, not to mention the problems arising from allergies.  I can recommend Just Smash Cakes who make perfect cakes for smashing and deliver them to the studio so they are ready and waiting for your session if you are looking to have one professionally made (they’re very reasonable) but of course, there are lots of cake makers out there that you can use.  Alternatively, there are some supermarket bought cakes that can be great – you just need to look and see if the icing is soft enough to make it smashable or you can make your own – I recommend fresh cream or butter cream icing as having the best squish factor.