You don't necessarily have to sell an entire rack to a company (or provide co-location services). We host two major hospitals at our hosting company. One company is using 6 load balanced servers and two other servers as backup machines (total of 8 servers). Our business with them started hosting a simple 5 page site for one of their internal labs and providing an external email. When their webmaster messed up their files, we had a backup for them. Shortly there after we were contracted to host two servers for them and it grew from there.
Capturing the larger customers has more to do with reputation and ability to deliver. If you tell a customer you can do something, you better be able to do it and do it perfect 100% of the time. We see many people promise things and then can't deliver. A true business model is to promise 90% and deliver 110%. We've followed that mantra for many years and it serves us well.
You WILL NOT get larger customers by sending out an email or sending a flyer to their office. You likely will not get them from a cold call either. Some of the best places for larger clients is job fairs, industry seminars and business events. Spend the money to get a booth (don't just pitch THEM at THEIR booth. Get a booth yourself, invite them out for drinks or a coffee. Have a game plan, and execute it.
TV and Radio are harder to get as the parent corporations usually provide some sort of service themselves. Information is king, so often the information posted on your local channel 4 news is shared with (or taken from) the parent NBC, ABC or other affiliate. So instead of going after the MAIN Radio station, go to the individual DJ's or voices. Offer to "live cam" an event and get some promotion that way. Be ready for them to TAKE your ideas and run it themselves - that's part of the game.