The series was part of that infamous DC Implosion in the 70s, where several series were cancelled without notice. #16 and #17 did get published, but boy, you'll have to go on a real hunt to find it.

http://en.wikipedia.org/wiki/Cancelled_Comic_Cavalcade

You almost could've had them all - albeit in b&w - two years ago when "Showcase Presents: SSoSV" was supposed to go on sale but I'm guessing it got cancelled along with the Captain Carrot collection as the two are still on "pre-order" when you search for them.

The Cancelled Comic Cavalcades weren't that hard for me to track down when I did it about fifteen years ago and that was before the e-bay explosion so hoping it won't be bad for you. Best of luck!

Gah! They cancelled the Suicide Squad Showcase around that time as well! Stupid economy!