OOH I am the person to help!!!!
Right OK the best pet shops lie in Ross on Wye - there are 2 - the Ark and Creature Comforts. Creature Comforts sells some fab cages, including the Imac Fantasy and used to stock the Gabber Rex but I don't know if they have any of those at the moment. The Ark sells some nice toys and the owner makes up little treat bags with plenty of mixed bits in which are very cheap
OK not technically Glos but close enough!
Lydney has an OK pet shop - it stocks a good range of toys etc
You might be interested to know that there is a show in Shurdington near Cheltenham in October