You can overexpress IKK by apropriate plasmid to induce specific activation of NFkB pathway in cell culture. 

You did not indicate whether you are looking for a physiological activator or not. If yes, it may be hard to find one. 

My understanding is that NF-kb is a multicomplex unit and not a receptor and it is activated by upstream signaling proteins rather than a direct ligands

Thanks all for your answers! As I expected, it may not possible to find a physiological activator (i.e., drug not plasmid)

Following

Following

Article NF-κB Regulation: Lessons from Structures

Well Dr. Ahmad Al-Moujahed , I feel (R)-2-Hydroxyglutaric acid disodium salt can be a good Nuclear Factor Kappa B Activator...