The Weaver gondolas were made in China, then Atlas O acquired them to produce more road names and road numbers.
There were a variety of O gauge gondolas and O scale gondolas produced by "K-Line" or MDK.
Williams by Bachmann has O gauge gondolas.
The original O scale Atlas O gondolas are available second hand. These gondolas were produced somewhere in Europe then imported and painted by companies like Weaver Models.
The new Atlas O scale Trainman gondolas are new cars made in China.
Andrew