At least per the hospital I work at, there's 5 registries.
Each has an 800 number. I only bothered to called Novartis since they were the first and I figured the gold standard.
Novartis 800 448 5938
Fazaclo 877 329 2256
Ivax (TEVA) 800 507 8334
Mylan 800 843 9915
Caraco 888 835 2237.
Per Novartis, they keep records permanently. A problem is if someone's been on Clozapine, and you have them for the first time, and you call Novartis, they might have been on a registry from a different company. This is certainly something where it may be better for staff members or the pharmacy to call for you to maximize your efficiency.
Where I work, automatically, all numbers are called whenever we get a Clozapine patient. If your hospital is not already doing this for you, I recommend that someone in your department get into this and facilitate a process where someone does this for the doctor.