Large amount of data on drop down list

Good day.

I have problem to load a web page with size of 7 MB.
Why the page has such heavy data to load?  Well, thanks to my vendor to put all the 12,000 supplier names on the drop down box.  

The supplier drop down box basically allows user to search the supplier name by enter the name on it and as you type the cursor will jump to the particular supplier on the drop down box.  Imagine, the page not just included with supplier drop down box but also product, material request code and so on.  Total 5 of such drop down boxes in a page.  As the supplier data increases, the page size will be increased as well.  In the end, how much Internet bandwidth do I need to run the page from multiple locations?  This is a nightmare to us!!!  The vendor keeps on saying that our Internet line is slow but to us, I would say their program is a "dinosaur" which hunger for large resources.

Hereby, I would like to seek opinion on the proper way of handling such design and shut the vendor's mouth off where giving us such nonsense excuse.

Thank you very much!