You could try contacting Monaco Coach, but I doubt if they have any manuals that go back that far.
Most of the manuals that come with an RV are individual manuals for the various appliances and systems, as supplied by the manufacturer of that item. You can download manuals for most Atwood, Norcold, Dometic, Thetford, Suburban, etc. appliance sand systems from the manufacturers site or other internet sites.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL