Where can I get a transmission mount?

Are you talking the crossmember or the mount? If it is just the mount 72 and down used one type and 73 and up used a spool type (and the crosmembers were different too). If you have the one from the 73 duster (doesn't mater which transmission 727 904 a833 etc) use that one. It is the best one in my opinion. Get the energy suspension poly bushing kit for it too.