You have a couple of different options here. You could get picked up by a broker who is already selling into the grocery chains and have them represent your line too. Without a track record though, that may be tough. You could also start with a small, local food outlet where you might have a relationship and start building a following. Once you get some traction and momentum going, then call on the appropriate buyer of one of the smaller or regional chains with your purchase data and show them that you have a following. They might be able to recommend salespeople who can help you scale. I think it will be much easier to leverage existing infrastructure than it will be to set up all of your own systems to sell into large chains so piggyback where you can and put your energy into creating demand for your products. Good luck!
With over 100 billion emails sent every day, it's getting harder and harder to stand out from the other scores of attention-seeking messages your customer deals with each day. But it's far from hopeless.