missing chunk number 0 for toast value 25693266 in pg_toast_25497233

I'm running into this issue again:

psql --version
psql (PostgreSQL) 8.3.7

COPY items_extended TO '/dev/null';
ERROR: missing chunk number 0 for toast value 25693266 in pg_toast_25497233

Unfortunately, I do not know where these are coming from and I cannot
replicate the data in at least one of my tables (which has 20 million
records) because of this. I've already found 10 bad records. There
are more.

I have four tables with 20 million records (and a fifth which has even
more) that may have this problem. Right now, checking every record
one by one is going to take *DAYS* to complete, and I'm in the middle
of adding additional nodes to our cluster because we are already
stretched to the limit.

I have a few options, such as trying to check batches of records and
spinning up multiple checkers in parallel looking at different subsets
of the data on wal shipped spares (assuming the wal shipped spares
would suffer the same problem, which is a big assumption), but this is
a lot of effort to get going.

Help!

Thanks,
Bryan