What you'll need to find are pre-1966 Colt Agent grips.
Up until 1966 the Detective Special and Cobra had the old long grip frame. The Agent was intended to be a minimal size deep concealment gun and had a short "Stubby" grip frame so it could have the smallest grips possible.
In 1966 all Colt "D" frame revolvers were changed to the Agent type short frame, only the DS and Cobra used grips that overlapped on the bottom of the grip frame.
So, shop for Agent grips.
In a pinch, you can buy DS or Cobra grips that fit the post-66 short grip frame and cut them off, re-checker and refinish them to make Agent type grips.