English native speaker to correct english in a presentation

I am working with a company that communicates in english although it is not our native language. All their Marketing Materials are in english and we would like to have them reviewd. The first work we need it is a small A5, 16 pages magazine with some text boxes, not to many, some graphics and pictures. It is not yet totally done, and for that reason I can not tell exactly how much text it will be.