I would give Inland Truck Parts in Irving, TX a call(they come right up on Google). They are also in the back of the FMCA magazine. Their prices are very good and their shipping is reasonable. I order a lot of filters from them. You also might try Napa Auto Parts. They've been able to cross reference most of the parts on my engine.
'00 Monaco Dip 38D
8.3L Cummins ISC