Thats it for this article. The only reliable option of this kind thats available is the Mingo get it on Amazon. Now hold them up to each other.
Make an identical cut on the other scrap piece using the same angle only reversed to the left or right as needed.
These include a saw thats suspended above the actual timber on a hinge. Otherwise it may tear away before you are finished sawing ruining the cut. A tenon saw would be ideal and even a cheap one will do. Chop saws are the simplest forms of mitre saws.