@thebf,
In New Mexico, we have what is called a "Child Support Bureau". Every state will have something similar and this should be your first point of contact.
For the past decade or so, courts have been requiring that support payments are made directly to that agency, and when the account becomes sufficiently delinquent, they should be getting withholding from the IRS. In extreme cases, they have gone so far as revoking licenses, even a CDL license for a commercial driver.
Hopefully, he still has the 8,000. If he doesn't, and he's in jail, the blood from a turnip thing might apply. Anyhow, get in touch with your state agency first. If you're in a town of any size, you probably have a local office.