Why does the Walker's Shortbread made for Starbucks taste better than the Walker's you buy in the store?

I am a shorbread freak. I am really not content with much of what I can find in this country. In Washington state, I used to get a locally made shortbread called Angus that was great.

I like the Walker’s at Starbucks, but it only comes in two-cookie packs. If you buy Walker’s at the store, it’s not as good (oilier).

I need help for my fix. Anyone got any ideas or great shortbread recipes? Warning: I’m picky.