Scotty cameron's website sells a variety of headcovers. I haven't seen the "art of putting" one on there in a while. I had that one on my putter but switched to the select model. 

I believe that they are available under the store tag on the Scotty website. However I think they are frequently out if stock. I am not positiv elf this though.

The original Art of Putting headcover is no longer available.  There is a new version sold at the custom shop (only) at:  http://www.scottycameron.com/custom-shop/classic.aspx

eBay may be your best bet.