I had a wristrocket that folded up like that when I was a kid. I think I got it at Kmart, but that was a very long time ago.

Here is a couple, mine was just like the marksman wristrocket. I really like the looks of the Barnett Black Widow model.

http://www.amazon.com/Marksman-3040-Folding-Slingshot/dp/B000MD68JM/ref=pd_sbs_sg_4

http://www.amazon.com/Barnett-17018-Folding-Slingshot-Contoured/dp/B003V8GOO4/ref=pd_sbs_sg_44

http://www.sausa.com/product.php?product_pk1=6

http://www.amazon.com/Daisy-Powerline-B52-Slingshot-slingshot/dp/B000N8KHLG/ref=pd_sbs_sg_27