There are custom juice companies that will mix to your taste. Do a search.
If you have ANY way to contact said person, try to, and try to find out WHAT flavors WHAT manufacturers, and WHAT percentages he/she used.
You'd be shocked at how many blueberry and shortbread recipes there can be made and etc. The cheapest way is to do it yourself but honestly UNLESS you know EXACTLY what the recipe is, your best bet is to try some premade blueberry shortbreads from different manufacturers and see if you get lucky.
I got a custom juice company to mix me in distilled h20 once, but I had to pick among THEIR flavors, and if you want to know why I even did it, well it was a win. It also turned out nicely. But, I can do better on my own, frankly, for pennies on the dollar.
Good luck, though.
Etc.
Anna