How do i get companies to provide me with a large number of sample items?

I am currently working as an orientation assistant for the college i attend. I have been contacting companies via email asking for large numbers of sample products for our orientation kits, so far all have refused. How do i go about getting a yes from these companies or are there certain companies in particular that i should contact???
Some examples of companies i've contacted are pepsi, durex, mead.

Don't contact companies via email - its much more professional if you contact them via an actual hand written letter.

Basically, import your Companies letterhead into the document at the top of the page.

Enter a couple of times, and enter the date

Then enter the companies address.

To whom it may concern

Basically in the first paragraph explain your company.

Next, talk about the event that you are requesting free samples for. Definetly mention just how much people their comapny is going to be exposed to if they provide samples of their products.

Finally, just quickly thank them for their time, and give them a contact number at the college.

Yours faithfully
(sign)
Your name
Your position.

I would think you are contacting the right companies, its just a matter of requiring a bit more formality.