There are a couple of series that have been written especially for preparing students for Trinity GESE:
Talking Trinity, Garnet
Garnet Education - ELT publisher
It needs a bit of padding and you will have to produce your own material for preparing students for the topic phase of the exam.
Pass Trinity, Black Cat
BLACK CAT PUBLISHING
I find that this needs some modification but is a good springboard for lesson planning and covers relevant language and themes
Good luck
Georgina