Well there are two things you can do for the shoes one just wear normal green and white tennis shoes or you can find plain white tennis shoes like his and paint the design on and add the green strap.
For the hat find a plain beanie hat (like this http://www.2giftshop.com/images/WT2222.jpg
(You may have to dye the hat though if you can find the right color)
And then glue or sew on the green things or what ever they are on the side then add the lime green trim to that. Then for the purple gem thing try finding a shiny purple fabric then cutting it out in a circular shape and sewing or gluing it to the hat.
Hope this helps!