Greetings, and welcome to the Forum!
Jump on in---the water's fine!
First of all, a 1978 Airstream is hardly an "antique;" it's practically a newborn in Airstream years. There are nuts out here who regularly buy trailers from the 50s and 60s, and use them hard. Fogetaboutit--- An Airstream can take it, and there's an abundance of parts available for 1978 models.
Second, except for the body itself, few parts of an Airstream were of a special manufacture. Therefore, suitable substitute parts can usually be found at hardware stores or RV dealers. I suspect that you can find a plastic bin in every size from 2" X 2" to 4' X 4' without leaving your hometown.
Finally, if you're gonna be one of those "keep it original" wackos (and you know who we are), do one of 2 things: 1) buy a trailer in original condition (and there should be plenty of '78s), or 2) identify the missing parts before you buy, and check with Inland RV, this website, the VAC classified site and e-bay for the availability of replacement parts.
Bottom line: you won't have to baby a '78 Airstream, and finding parts will not be hard. Join the club! Good Luck!