Hello and thank you for your question.
Experts on the site are not allowed to perform searches for specific persons, such as your son, however, I will try to provide you with resources that may help you in your search.
I note that you have searched the public inmate database, so the next step may be to contact the Department of Corrections. The Family Services Division can be found here http://www.doc.nv.gov/?q=node/7
They also list contact information for Friends and Family of Incarcerated Persons, Inc., a private organization that supports incarcerated persons and their families. I realize that your son is no longer incarcerated and on parole, but these places may be able to help you, or at least, suggest who can.
In addition, you can search the Interstate Compact Offender Tracking System (ICOTS) https://pwp.interstatecompact.org/PWP/
as all parolees
who transfer supervision to another state are listed here.
Finally, you can contact the parole office that your son went through. The offices and contact information are listed here http://npp.dps.nv.gov/Contact/Contact_Information/
The parole office would still maintain records, even if direct supervision has been transferred to another state.
I wish you luck in your search and please feel free to ask any follow-up questions.