Harbor Freight, Woodcraft, any woodworking store...probably even the box stores have them. It is a very aggressive carving bit that goes in a rotary tool...you can have some real fast fun with those.
My computer is way too slow...I was going to show you one. Do a search for "typhoon Burr" there is a ton of options, sizes, shapes...they can be cheap or expensive...you don't need expensive for worthless wood. Sometimes you can get a whole set at HF of typhoon burrs for 5-10 bucks.
Don't get me wrong either...your blank looks really super...the typhoon comment is just a tip to make it even better, because then you don't just have to always have that perfect piece of wood for the job...you can mangle up your own piece.