You could always create your own brush.
Use this for starters.
1) Save and Open the file in photoshop.
2) Select All (Ctrl + A)
3) Select EDIT > Define Brush.
4) Give it a unique name.
You could add a gradient filter to give it the rainbow effect and use various brush sizes. You may have to either create various brushes or get creative with rotating the layer to use it in different angles.
Here is a quick 20 second sample.
Michael (imaginemn)