You can find the 2013 Morgan show rules at this link
http://www.USEF.org/documents/rulebook/2013/19-MO.pdf
The shoeing regulations are rule MO-103 . The updates are already included in the 2013 USEF Morgan rules.
If you are showing in the Morgan horse division of a USEF rated
horse show, then you are responsible to understand and
follow the division rules published in the USEF Morgan rules.