Talk about being lucky.
We reviewed the tables that were almost out of headroom as far as PK identity values hitting the limit of an int, and found that for the two tables that were almost out of room, the PK's were not FK's but were simply in there to satisfy the basic rule that every table should have a primary key.
These tables had only 20-25,000 records; it was only the fact that they were migrated from a replicated Access database that resulted in the very large autonumbers.
Therefore, for both tables we could just go in there & drop the existing identity column & add a new identity column with a seed of 1 and increment of 1. Problem solved.