We looked at Barth travel trailer double axle...it was supposed to be 21' but seemed longer than that.Does anyone know the types that were made that year and can you still find parts?

In most travel trailers the running gear, appliances & accessories are generic. In your older Barth TT that is almost certainly true of your appliances, though what is there may be obsolete.

The running gear is something else. Barths were limited-production, often built to order. Their suspension may have been unique, though wheels, tires, brakes, etc. are most likely standard.

The odds are that appliances, wheels, tires, etc., are off-the-shelf items readily available, though some may be obsolete. Most, but perhaps not all, obsolete items will be replaceable.

The coach body is unique, & of top quality. Any necessary repairs on that will be a custom job. It is unlikely that there is anything else, except possibly the suspension, where parts would not be readily available.

The only way to be really sure, is to examine the unit & get advice from a KNOWLEDGEABLE RV repair person.

If the unit does not require total restoration at vast expense, or if it does, and you enjoy restoring high quality mechanical artifacts, there is no better base to start from than an elderly Barth. There are few coaches of any kind that could stand a total gutting, & be rebuilt from scratch, & be as new. Barth is one that could.