hey i know this is kinda lame question but...

[Shindy]

What are the stone cylinder structures infront of usually stores or parking lots called?

is there any store that sells caps for them? preferably a famous one?

[Flibbo]

I think you mean those things to stop cars ploughing into the store window? I think they're called Bollards but that might just be the nautical ones used at docks and piers. I can't say i know anything about caps for them though. Are you planning a prank or something?