Spotted this in my local store, and there were various offers on Disney Cars,Planes etc... too. A full stand specifically designed to promote the offer.
Thomas take n play engines - Harvey, Porter, Stephen, Thomas, Percy and Salty !
It's not the cheapest you'll ever find, but given this is national, it's not a wild goose chase, and Harvey/Porter/Stephen/Salty aren't going to be found in many supermarkets going cheap, it's a good stocking filler/ birthday present for the organised!
I've checked and it appears to be store only - not online.