I'm not sure what you mean about the "tuning system" for the Mongomery Ward radio. It's a superhetrodyne radio with IF stages and the RF stage has a variable capacitor for tuning. Mongomery Ward didn't make radio chassis but instead purchased from an OEM. You can sometimes identify the chassis by its tube complement and component layout, but it's a manual process of looking through all the schematics in a collection like the Rider schematics.
As for Trans-Oceanics parts, your best bet is to find one on eBay that you can use as a parts mule. If you just want tubes and capacitors, you can buy those separately from a electronics supply company but if you need the cabinet or knobs or dial - things unique to the Trans-Oceanic - then you'll need to buy a parts mule.