Try this:

1) Write a single page letter (or email) that describes not whats on offer but the sort of offer it is - i.e leave mystery to the question

2) Go to their website and find 6 people who might be in charge of answering the question (Senior VP of this, director of X, etc)

3) Print 6 letters and highlight one name on each letter and put them into 6 envelopes and write the highlited name on the front

4) Phone the company and ask the for mail room - and ask his name

5) Fedex the envelopes to the guy in the mailroom and request "please distribute" - it's his job to distribute them so he will

6) Each of the 6 letter will get delivered and when they open them they'll see the other names on the letters, so they have no recourse but to phone the other and find out who is going to deal with your letter - one of them will invariably contact you to find out what you're offering

This will save you tons of time spamming email boxes and cold calling - each time I've tried this it has worked