I cut a 1/4" thick piece of stock from one of my leftover pieces of redheart, drew out a rough shape of one fin, and cut that shape out on the scroll saw.
After some careful sanding, I was able to fit the curvature of the fin to the rocket body.
I traced the finalized fin on the remainder of my 1/4" thick slice 3 more times, then cut those out on the scroll saw. I sanded the remaining 3 fins to match the first one.
Unfortunately, I have no images of this process.