hornby recently told me percy will be back in stock now, and toby at the end of august, could he have possibly gone for soem work done to him or a re-model??
Probably not. It's most likely that the models of the last batch sold out before the next ones were ready. Model railway items are not (in most cases) produced in enough quantities to have them continually rolling of the manufacturing lines. Rather, they'll produce one large batch of models, even if the item is not officially a 'limited edition', and the models then sold. In the case of items like Toby and Percy, where there will be enough further demand and a lack of an alternative name/number, they will produce further batches, but these still have to made, packaged and distributed, which takes time, during which the stocks of the last lot can run out.
And Rocketman, not everything in the ranges is fictional. Most of the rolling stock for both companies is formed of older models from the main ranges (in Bachmann's case they use old mainline toolings), and several of Hornby's engines (Thomas, Henry, Duck, Oliver, Stepney, D7101, Spencer) are of the right class for the character, using older Hornby toolings.
Not sure what the scale of the Bachmann stuff has to do with anything mentioned - the only reference to scale was I believe the over-scale nature of Hornby's Toby.