Good advice is worth every penny you pay for it. Free advice is worth the same.
With that in mind, talk to the US Small Business Administration. They have an office on North Keystone in Indianapolis.
They can help you find a business mentor, or lead you to lots of information.
From personal experience I can tell you that some of their information is useful, but not all of it. Trying to separate out the gems can be a job in itself.
Get a couple books on marketing from your nearest library. They may not teach you much, but you might pick up some of the lingo used in that trade. You might even find names of companies you would like to consult.
The irony of your question is that a good marketing advisor/company should be doing such a good job of marketing themselves that you would already know who they were. If they can’t market themselves, how can they market your products? So, if you have to ask about marketing, then there must not be any good marketing firms around! It is a paradox. Good luck in your search.