Acting on a tip from another listmember, I called CA Imports in Washington.
They DO  have the elusive crossover pipe we've all been looking for.
They have all the rest of the exhaust components too, although not the
elbow.  RMMW does have the elbow, though.
Here are the prices I got from CA Imports:

crossover pipe    $249.92

cat convert       $129.94

muffler           $97.97

tailpipe          $14.95

assorted gaskets  $10-$12

Actually, now that I look in the RMMW catlog, they DO NOT have the correct
elbow for the 79.  Anyone know if the crossover pipe actually wraps 
around and connects right to the cat convert?  

Enjoy, 
Paul