I found this artist at the Portland farmers market - she makes some really nice marbles!
http://www.ejhotglass.com/
Her artistic talents transfer around to the other side of the glass too - which is unusual for this type of marble....most artists just create the flower or the scene facing you and leave the back side blank or worse - EJ creates a decent pattern to see on the opposite side so that when you turn the marble it is just as beautiful.