To add to Tom's comments, a source of difficulty in refurbing an older trailer is that "they don't make em [and the stuff that went in them] like that anymore". You may find a vintage appliance, light
fixture, or whatnot listed by a very few rv salvor/resellers on private internet sites or on eBay. For a utilitarian refurb, much of this stuff probably isn't worth the chance you take on condition or the price you pay for rarity (consider the Bargman L-400
lockset which is set in a custom molded recess in older Burro exterior doors and seen occasionally priced above 2C$.) You may have occasional success running on to someone who is parting out their trailer or replacing something in it that's still usable. An example would be sets or partial sets of cushions for specific trailers found with fair frequency in the for sale
ads on this site.
Tom's choice of the word "generic" can't be overemphasized. There are plenty of 3-way fridges, range tops, electrical
components and fixtures, windows
, running lights
, couplers, axles, water pumps and tanks, furnaces out there NIB. Some few will not have changed all that much in footprint or dimensions, method of installation from "earlier" models. Others will. You will need a good eye for specs and a tape measure to avoid "don't fit" surprises. You may also need the willingness to engage in "cut and fit" and the structural and cosmetic corrections necessary on either interior or exterior.
Specific to "sourcing" the upper bunk in the Burro, the "factory assembly manual" reveals that the materials and mechanisms necessary are not exotic or special purpose but the sort of thing available from your big box hardware/lumber seller (plywood, conduit, pipe, or plated closet rods, floor flanges or end hangers, butt hinges and locking mechanisms. If you can hammer, saw and make cushions, the world is your oyster!