The best replacement would probably be Hall sensors though I'm uncertain what effect FF would have on their functionality. 
Here's what I found regarding ratings: 
Force 3D/Strike Force 3D  
DigiKey: 963223-KIT-ND FORCE 3D  
DigiKey: 963191-KIT-ND STRIKE FORCE 3D  
RES,VAR,100K,50DEG,+/-10%,PLAS 3 X, Y, Twist  
RES,VAR,100K,70DEG,+/-10%,PLAS 1 Throttle  
Extreme Digital 3D  
DigiKey: 963193-KIT-ND EXTREME DIGITAL 3D  
RES,VAR,100K,50DEG,+/-10%,PLAS 1 Twist  
RES,VAR,100K,70DEG,+/-10%,PLAS 1 Throttle  
RES,VAR,100K,50DEG,+/-10%,PLAS 2 X, Y 
and straight from the horse's orifice - DigiKey