Have you tried to reverse engineer the Charbroil rub? Start with a rub recipe that has most of the same ingredients and add what is missing?
I have not, I was hoping that somebody would have one that they have bought that was similar. Not sure why they discontinued it, it was a really good rub.
The short answer is Charbroil discontinued the rub because it didn't have enough sales volume. I spent nearly 25 years working in the food processing industry and the only reason I've ever seen a product discontinued is that there weren't enough sales to make the product adequately profitable. As much as you like the product, apparently other people didn't.
A tip on reverse engineering the rub. If you look at the ingredient list, the list is presented in order of decreasing quantity by weight. So, if salt is the first ingredient, there is more salt in the rub than anything else. If sugar is the second item, there is less sugar than salt, but more sugar than the third item. One of the ways to find a comparable product is to find a rub with the same ingredients in the same order on the ingredient declaration. (I'd think there is a pretty good chance that there is a comparable product on the market. Obviously, Charbroil isn't making this product themselves. Someone is doing it for them. And there is a pretty good chance that this is a product someone else is making that simply has a Charbroil label on it. Or a variation of what someone else is selling with an additional ingredient or two. Read the label carefully and it might give you some clues where it is made or who made it. If you can identify a location, look for spice or seasoning companies in that geographic area.)