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There should be option called ipv6, that may let you create 100 Ipv6 Proxies with just one instance.
Here -> https://createproxy.com/dashboard/vultr/ -> Select any ipv6 option.
Please note, that it will create you exact number of IPv6 Proxies that is specified on page where you can add VULTR account, please note, that you should not set more then 100 ipv6 proxies per instance.