Here are a few thoughts. Given the product type and market, but without knowing exactly what it is, I think your biggest hurdle is going to be to have a prototype made and then tested against a myriad of Federal, State and Municipal regulations, and pass all of those regulations.
While you are doing this, go to the same tradeshows as Galls is exhibiting and look at your competition. Even if you have a unique product, law enforcement still has a fixed budget and you will need a compelling story to get them to reallocate funds to buy yours. Your product will fit into a budget category. You need to determine that category and an estimate of region-by-region budgets.
Also pick up all the magazine trade journals that LE product buyers and recommenders/influencers read.
in this regard, it would be good to have a "test town" using your product for free for a year and have the chief of law enforcement write you a letter of endorsement that you can use in your marketing and sales efforts. This person will become a shareholder BTW.
You can do your own patent search but it will be best to hire an IP law firm that specializes in LE products. You will spend between $1K for a mark search and up to $50K (or more) to go through an entire patent process.
My guess is that only after you have X towns using your product will Galls be interested. But it doesn't hurt to go to them after you have a product made, butbefore you go to them, make sure your product is well-protected.
If your product saves lives or better, saves money for LE, plan on a major
PR campaign once you can demonstrate that.
If you want to talk more, feel free to email me.
Good luck.