A Yamamoto will flat spin. [Sort of.]

Move the CG back until it is just controlable in pitch at the end of the flight. Get max rudder movement and max up elevator movement. 45 deree minimum on both. You WILL NEED RATES AND EXPO !

Enter a spin as normal. Feed in FULL power and while holding full up and full rudder feed in some opposite aileron. It is likely to be easier to do in one direction.

But as everyone else is saying if you want to do 3D get a 3D plane. A Magic or a Cougar is a good start but profiles are best IMHO.

Just sold my Moris Hobbies Sledge which would do an inverted climbing flat spin.