Start your pitch to the producers not the management. If you're pitching a hospital talk to the doctors/nurses. Bankers for a bank, and associates for a law firm. Don't ask for management or the person in charge. I've dealt with a lot of organizations at a high level. Trying to jump in line and go straight for the CEO will get you lost in the noise. The bosses are already bombarded with requests promising everything.
You need at least one good producer to back you. These people are a lot easier to reach. They aren't usually sold too, and generally are closer to the pain points ("pain points" flow downhill). Once you have someone on the inside to vouch for the idea, then start moving up the chain.
Take this advice! The people that are actually suffering from the problems your business solves are (usually) not managers, CEO, or anyone at the top. It is the people in the middle or bottom. They are usually also so happy to have something that solves their problems, that they will act as an internal champion for you during the sales process.
You haven't described the service you're offering, so it's difficult to know for sure where to send you. If your service obviates the need for a marketing team I wouldn't recommend it (even if it's marketing based).
For a walmart/bestbuy I'd try to win a single store first if that's possible. Or target a smaller competitor and use that as leverage. If you're trying to sell to an entire F500 at once, I'd probably say you need to change scope. Perhaps there is some way to piggyback without their permission? Making it so they can't ignore you.
Large retail companies have "buyers" or "merchants". You want to contact them. Product samples, schedule calls, and be prepared for face-to-face meetings which should be Goal #1 (that's where you will close the deal). If you don't already know - Ask them how they view their average Consumer, then prove to them why those Consumers will love your product.
Make the risk as low as possible for them. Fund the inventory, fund the advertising, etc. - these are things they will try and negotiate. In the end, business is business. If they think their Consumer may want your product and the risk of trying it out is low, they may just move forward.
Bonus:
The chain typically goes like "assistant", "associate", "buyer", "manager", "vp" jump in the middle (or lower if you need to) and work your way up.
EDIT: Also there are Vendor Rep companies that have these relationships. This may be something you want to consider.
Be careful with this tactic. It is easy to have all your time sucked away by people who are easier to reach and convince because they have no influence. Expect to have a high level of non-producers but if a couple work out well you are in good shape.
I often go straight to the C level. Even if it is to get blown off and have them tell me, "John Doe handles that for me." I then talk to John Doe and say, "Hey, Mr. CEO told me to talk to you about..." They listen, but show value quickly before they realize the CEO just handed you off to them.
You need at least one good producer to back you. These people are a lot easier to reach. They aren't usually sold too, and generally are closer to the pain points ("pain points" flow downhill). Once you have someone on the inside to vouch for the idea, then start moving up the chain.