All right, I'll explain the street vendor.
Sometimes, a notice may appear on the Tama News Board saying "Here comes the ______ vendor!" That notice means that in a few days that vendor is going to appear on the central pavilion of TamaEXPO, around where the Ecology Pavilion is.
When the Tama News Board says, "The ________ shop is open!" it means that the street vendor has arrived at TamaEXPO and should appear at the central pavilion. If the street vendor is still not there even though the Tama News Board says, "The ________ shop is open!" then the problem should be solved if you enter and exit a building.
I have some strange feeling that the times the street vendor comes is related to how often certain games are played.