In general terms Marketing... in order to increase sales, people HAVE to know your product exists and where to buy it.
Now how to get it into Physical Retailers., well that's a little more difficult because in general terms most Retailers do not purchase products "Directly" per se... instead you're usually dealing with a Logistics and/or Wholesaler whom you trust.
So, for example within my Parents Pub (and this is true of many Pubs) they only stock products from a Tesco Subsidiary called "Bookers"
The Retailer that I currently work for gets our Products from AF Blakemore, Costa and Country Choice.
In fact as the Assistant Manager, I'd quite often see Company Reps coming into our Store trying to essentially upsell us on Brand Specific Displays, Branded Equipment, New Products, etc.
And what I *HAVE* to tell them is that., our Stock and Displays are all determined by Head Office and we Order based upon what they make available through our Logistic Channel; and they also control what Promotions we run, with orders being entirely at our digression as to what WE need in said Store.
And this is something you will likely hear a lot, outside of Independently run store... but then their footfall and sales are likely not going to be useful to you.
What you'll need instead is to go to various websites of Chain Brands and find the number of their Purchasing Department., as they will handle Purchasing; and then your aim there is to try to sell them on your Product.. as in what Quantities you can Product., where they can be shipped to., etc.
Trust me before dealing with such, you're GOING to want to be able to answer anything they could possible ask; as such be sure to have your Production, Logistics and relevant figures all squared away.
Outside of that, there is nothing wrong with going "Independent" via Amazon or NewEgg.
These are legitimate market place business' that you'll be guaranteed (esp. if you have low competition of similar / same products) to have a larger audience that you can reach without expensive advertising... although also remember you can purchase to be a "Featured", "Partnered" or in Amazon' case part of their "Prime" Products.
Beyond this there is always creating your own Digital Storefront... things like Squarespace and Wix are cheap to get; and very simply to create; then advertise on Facebook, Twitter or Forums for people looking for such products; just to get that word-of-mouth out there.
Then of course there are always the Traditional Market Stalls., most places have a County / Local Market that is run every Week or Fortnight; and it's usually trivial to get permission to have and setup a stall to begin selling wares.
The key here is to target what will net you the biggest audience from which to grow., because as you do... this in turn will open up new options.