I found mine on eBay used. There seems to be 2 slightly different styles. The one length is not as long as the one you have in your picture.
These were the ones I found.
http://67-72chevytrucks.com/vboard/a...1&d=1525747686
I feel pretty certain I found some new ones after I found the used ones but I've racked my brain and can't remember where.