trouble with MR4800 cutting deck

[North farmer]

Hi folks....I have a B6100 HST that has a mid mount MR4800 cutting deck. I am having trouble with the drive pulley located on the deck,that is mounted below the gear box. The key in the pulley was destroyed and broke the square channel inside the pulley that houses the key, so the pulley spins freely on the drive shaft . I am afraid because of the age of deck that I wont be able to source a new pulley. Does anyone have a parts breakdown of the drive unit so I will know how it goes back together when or if I source a new pulley? thanks