I know crower makes a stroker kit for b16 and b18. Does anyone makes a stroker kit for the b20?

 

The B18B stroker kit would work, you would just need to get the proper pistons(84mm) I'm not sure you would want to do this as it would make for a very poor R/S ratio similar to the old B21 prelude motors however, The lighter reciprocating mass and stronger componentry might balance this fact out. Leaving you with the same redline with a nice increase in displacement. 2.3 liter B series sounds yummy.
Do more research on the B20 motor, it is very similar to the B18B series motors.

 

There is the issue of where the rod actually conects to the piston......

On stroker kits the raise the rod higher into the piston.....