Thanks for the reply.
Im looking for a 12L075, basically a 12 tooth pulley to suit a 075 (19.1mm) belt with a 6.35 or less pilot to suit a nema 23. I really dont understand what consequences changing the pulley will have, I have emailed the designer and waiting for him to get back to me (he is very responsive by the way). He had to use a bush when building his machine too but it was a different size to the one I would have to buy from the UK. I did ask about the bush in the first place and he told me he got it from a local hardware store.

Is it me or do the hardware stores in the USA stock everything!!!!!!