OK. There is an organization that does child support collections.
The number is 1-800-801-KIDS.
They don't get paid until you do. However, they will keep 20 to 34 percent of the back support collected.
There is an application fee, but they will do two demand letters free.
Hope this information is helpful.
(I wish the child support courts also had a "collections" arm, but that is left up to the parties involved at this time....)