Was it repo'd? I KNEW they were on a smaller budget in S3, but that is just sad.
For a long time, people speculated that the Romulan ship from Season One had been stolen and, when they needed a Romulan vessel in Season Three and no search had turned up the Romulan ship model, they decided to go with the then-just-newly-built Klingon ship model and add the line to the script about tech sharing.
However, I read one theory, a few years ago, as to why the "stolen"/"missing" model has never materialized in any private collection. Supposedly the main hull of that Romulan model was plaster, not the usual wood/plastic/whatever, and it had been accidentally dropped - and smashed to smithereens.