Forum Moderators: buckworks
Its impossibly difficult unless you have a previous relationship with the buyers.
Ever consider displaying your product at a trade show where you know the retailers are attending? Its an expensive gamble, but it does work. I attend trade show several times a year, often I will see a brand new product and 6 months later I see it on the shelves at a large retailer.
As for my own ideas, I feel like the best way to attract "big companies" is to be a leader in your industry - great product/service, great customer interaction, great reputation. Ideally, they will eventually come to you. Of course, this is not guaranteed, but I like to think in Pollyanna-ish ways.
When you do contact these big shots, though, be professional and CONCISE. Don't send unsolicited letters/e-mails that are longer than you would take the time to read. If you make phone calls, keep the pitch short and sweet. If people feel like you're taking up too much of their time (even with extremely useful information), that's just not a good thing.