Are you trying to stop the texting, or to find out who is doing it?
For the first, you can file complaints with whatever company or carrier is hosting the numbers. No one's going to give out information other than pursuant to a warrant or subpoena, however, so you either have to steer law enforcement to issue one of those as part of a criminal investigation, or get a lawyer to do it as (likely) part of a civil one.
What is your process to sue spam callers? Is it repeatable/scalable?