i believe the mazdaspeed shift knob uses a different thread pitch than what your Pro5 uses. so you may need to replace the shifter as well. it would be a great time to upgrade to a shortshifter and then find a knob.
However, i may sell mine, because i am not sure if i want to use it. so i have the MSP shifter, a mazdaspeed knob (not the sparco one) and a yellow stitched shift boot. make me a great offer and I may sell then instead of installing them on my car.
As for the Racing harts, you should check the for sale section every day in the mournings, i got lucky and foudn a set, but once they are posted for sale you need to buy them asap. Good luck Matt