I think there's one.. goes along the lines of HCF, B + P but I dunno, this shortcut seems kinda iffy.
If you want to link a Stand C into his rush DM Ryuko Ranbu the easiest way to do it is this way:
QCF, QCFD (that means to roll the joysticm from forward, to down-forward, to down), C, QCB + P
This will allow you to combo his crouching C into his DM in one motion.
If you want a shortcut for his stand c, fwd + A, rush DM combo, a fairly easy one is to do a dwn C instead, hold C, do QCF + A, let go of C, then go hcb + P. holding C will allow you to do the QCF + A motion without releasing a special. The game will still read it as a QCF motion, but just not as an indication to do a fireball, just his command attack.
Me? I used to use the shortcut, but now I just do Takuma's combo manually. More easier and looks more "skillful".