You might try calling Gary Jamison(dealer) at 570-253-4810.He is about the only dealer that has parts for Yanmar decks.
My YM186D came with a YCM60 deck,and I like it,but it can't lift high enough because of the front drive shaft,and you have to avoid rough ground.
Do you have the electric clutch on the front of the motor? Woods also made a MMM for the 186,not sure if it ran off the front clutch,or belt driven off the PTO.