Second Manufacturer box

Does anyone know how we can create a second manufacturer box? What we would like to do is:

• Add manufacturers through the first manufacturers list
  
• Add clothing sizes through the second manufacturers list
  
• When creating a product, select the manufacturer and clothing size for that product.
  
• When using the advanced search, add the second manufacturer. When a selection is done in the first box, filter the second so that only the sizes available for this manufacturer are displayed.
  
  
  
  Maybe someone has already made something like this and would like to share it… or give us a help how to get started…

In the modding development manual I’m writing and almost done with volume 1 you’ll hopefully be able to read the manual and make this mod work by yourself, it will take a little trial and error but you’ll have the steps of what to do and can be done with a little work…