You might try to do a "reverse engineering" thing. It may take quite a few times but I'll bet you will come close or create a sauce you like even better.
When I want to make a sauce like something I like that is commercially available I first read the ingredients list on the label. The ingredients are listed in order of volume i.e. if the first ingredient listed is catchup and the second is brown sugar then you know that those are the two main items to start with. You can go from there to find the other ingredients.
I'd also recommend training your taste by tasting a lot of spices just by themselves so that when you taste a sauce or rub you have a good idea and starting place to build the flavors of what you want to create.
There are a ton of BBQ sauce recipes that you can Google and when you find one that has a very similar ingredient to the sauce you want to clone you can experiment with the flavors until you have something you like.