Email for a provider

John told me, he was talking to you about the forthcoming fair and we want to know if (, due to the closeness,) we can help with something. Please let us know as soon as possible so we can make preparations. (in order to prepare it.)

Closeness is a little ambiguous in this sentence. It can mean relatively close in terms of distance or in time. I guess you meant closeness of time, so you could use 'forthcoming' which means something which is about to happen soon. 

If closeness relates to distance:

John told me that he spoke with you about the fair, and we were wondering if there was anything that we could help with due to it being close to our location. Please let us know as soon as possible so that we may make the necessary preparations.