With the type of quantities you will be looking at, your spice supplier(s) should be glad to provide you with a quote for your formula (or part thereof).
Working with them will also give you a good idea on your product cost (at volume).
Most do their own packaging or work with packaging companies.
I do know that some proprietary product (like yours) have part of the recipe blended with one company and finished and package at another.
In some of our local restaurants, small seasoning companies have product on the tables for customers to try on their food or are used in their menu features.
It is an easy place to start.
I did some research on amazon a few years ago for a product we were taking to market (non-BBQ related), what I found, well, do your homework before jumping in on that one!
And yes, get some "credible feedback", Brethren, comp team opinion, or otherwise.
Just my .02.
-Brick vert smoker, Tuscan wood grill
ECB-sent to the curb!
"When it comes right down to it, you just want to be surrounded by good people and good food."