Getting IPv6 address with an IPv4 address?

Hi. I am working on an application that pulls the client IP address, and checks Wi-Fi RF health against our wireless controllers based on the client. I am able to get the client's IPv4 address, but the issue is that sometimes only an IPv6 address shows up in the controller, so I am having a bit of trouble searching the controller for the client since I only know the IPv4 address. I am able to ping the IP and get the MAC address via arp, but haven't been able to figure out how to go from IPv4/MAC to discover their IPv6 address. Could anyone point me in the right direction for that? I've tried a few tools like ping/fping, arp/ndp, dig, nslookup, etc, but nothing seems to give the info I need. Thanks in advance for any assistance!!