I have done a basic search on the uspto.gov website, as well as an internet search, and have found nothing to dissuade me from believing that my slogan has not been used. I know there are other search avenues to which I may or may not have access, but allowing that this slogan has not been used before, how would I best protect it while I am trying to attach it to a product or service? I truly believe it would sell well on its own, but I think a larger business entity (e.g. Adidas, Converse) would want it for their own. I fear I will be the guppy that is swallowed by the bigger fish in the tank.
A slogan should be developed based on understanding the benefit most desired by the target audience for a particular product or service. So creating a slogan and then trying to find a company to fit it is working backwards. Most companies that market through the media have agencies or creative teams in place to develop their core messaging, and I've never seen them buy a slogan from an outside entity not involved with creative development for them.