To be clear, you want to limit only one IP or IP range accessible to the port 5060 and 10000 on WAN?

You can go to Luci->firewall->traffic rules, find your port forward then edit it. You will have a lot of options.

More advanced, you can try some IP tables skills. Like this one: https://www.cyberciti.biz/faq/iptables-block-port/