What do you call the pieces that are put underneath carport post that are on a slab and where do you get them?
Summary of key words: post base; Simpson; stand-off; embedded 

They didn't know what it was, even after showing them the picture because Home Depot people are almost never experts and often not even that knowledgeable about construction.

What you are looking for is called a post base. In particular, it sounds like it's a stand-off type which means that there is a riser at the bottom. Also, that it is likely an embedded type, which means that it was cast into the concrete when the concrete was poured.

Since you can't place a cast-in into cured concrete, you'll need the type that uses bolts placed into holes pre-drilled into concrete.

Simpson brand hardware is the most common and there are other brands. They are lots of different options. To find knowledgeable people, I suggest going to your local lumberyard or building supply, not a home improvement box giant.