You can make your own in less than 10 minutes.
Step 1: What You Will Need
-A Piece of Cardboard/Poster Board (Anything will work as long as it can fit in your shirt and you can bend it)
-Fabric Paint ( I am using Acrylic Paint. Fabric Paint will stay on the shirt longer and is machine washable friendly)
-A plain t-shirt
Draw a line down the left side of the shirt on the poster board.
This is your cutting line.
Cut the poster Board.
Step 3: Fitting the Poster Board in your Shirt
Cut the board more to make it fit better if it is too big.
If it fits, take the poster board out of the shirt and fold it in half, long ways.
Put the poster board back in the shirt.
Notice that the fold is in the middle of the shirt...
Thats where your fold should be.
Step 4: Paint and Fold Shirt in Half
Use your paint and get creative.
Dont try to make something.
Just let it flow.
You can put the paint anywhere on the front of the shirt.
Once you have painted your shirt:
Fold the shirt in half. Be careful not to let the shirt slide around when you are folding it.
Step 5: Carefully open your shirt
Let the shirt dry before removing the poster board!
Once it is dry remove the poster board.