I meant to ask: Are Tunnock's tea cakes available year round in the UK?
In the U.S., the equivalent cookies aren't made in the summer, because they melt.
The two American variations that I know of are called Mallomars or Pinwheels, both by Nabisco. The Mallomars are shaped like Tunnock's tea cakes. The Pinwheels are scalloped and fancier shaped.