I never heard of them, but I think it would be cool to have coaster place cards. I'm sure you can make them or go to any favor shop and they could provide them.
I just googled 'flat placecards'. You can also purchase nice cardstock paper from a stationary store and have Kinkos cut it to the right size. They will also print them for you. It's a pretty inexpensive way to do placecards.
I just googled 'flat placecards'. You can also purchase nice cardstock paper from a stationary store and have Kinkos cut it to the right size. They will also print them for you. It's a pretty inexpensive way to do placecards.