The template I use is really just the "It Came from the Desert" back insert, available for download from the crazybanana.tk website.
The style is more in tune with the HuCard releases than the later CD releases so it works well for those carts that didn't come with cases originally. Of course, I blacked out the "CD" part of the TurboGrafx logo and removed the mention of "CD" from the back.
"It Came from the Desert" contains half the letters in the alphabet, and constructing others (L from I, N from M, etc) is pretty easy in a PhotoShop-like program.
If for some reason you don't like having the green tab on the spine you can change the color to whatever you want.
I just use generic empty CD cases you can pick up many places for like $0.25/ea, smash out the small CD retainer pins inside with a hammer and insert my fresh back insert into the case. They turn out looking pretty nice on the shelf.