What sort of data are your customer supplied data and the data from your company? Tables of locations (csv, excel, etc.)? Polygons? Since a dual axis map will only let you see two axes at once, it sounds like you'll need to figure out a way to combine two of your files. If your customer and company datasets are both just point locations in text tables, you could combine those and symbolize separately in a single layer, and then add your sales territories on a dual axis map.