UKARA is a defence (not a licence), which allows you to purchase RIFs, providing you are over 18 (which you need to be to purchase IFs or RIFs anyway).Ownership doesn't matter, so you don't need UKARA to own a RIF. The possible ways you could own one without defence is either it being gifted to you, or purchased before the VCRA came into effect in 2007.
There are also other defences available, although UKARA is the most popular and most recognised.
To purchase a RIF, you actually only need to prove you skirmish regularly and are over 18.
Being a registered reenactor is also a defence which allows you to purchase RIFs.