As another newbie, I'm going to put in my 1/2 cent worth.
1. Check if Bachman offer's a HON3 version. If so, theuy would be your best source of parts.
2. MDC makes HO and HON3 Shay kits. I have a HON# kit, UNBUILT, but I don't know if you could swap any parts.
3. Check with NWSL , as they have a lot of HON3 drivers and other parts. They may be able to tell you if it is EASILY done.
Good Luck!!!