It isn't a full exploded parts breakdown, but the Cultivator Operator's Manual has pretty good illustrations of the attachment. From it, you should be able to identify all the major assemblies. If you don't have that manual, look in the PDF manuals (under Quick links at the top left of this page). Go to:
McCormick-Deering Implements and Attachment Manuals
then download:
McCormick No. 144 Cultivator 1 011 803 R2 11-12-59-3B
The fertilizer attachment is in the last 4 pages.