[Mike]

Bob, once you have done the set up on your router table you should get consistant tenons. Just remember to use a backerboard to prevent tear out.

 

[Mike]

Rockler or Woodcraft both stock tenoning bits. Adjustable tenoning bits are made by Freud & Amana.

 

[Mike]

Joe, I viewed the Amana adjustable bit in an ad in The Woodworkers Journal. I believe the Freud bit was in Popular Woodworking, and I am pretty sure I saw it at the Performance line tool store in Warren, MI. http://www.performancelinetool.com/
These are relatively new bits.