Based on what little I know about where parts were farmed from, the Vickers airframe and the Rolls-Royce engines are well documented in several prop builds.
I presume they had the airframe and engine(s) out behind the model shop, and the prop guys would go looking for "cool stuff". So, it stands to reason (in my mind) that any on the fence decisions related to origin should lean in those directions, until proven otherwise.
That of course does not make them any easier to obtain, but there is at least one HUGE aircraft graveyard in Arizona that I have seen where a Vickers might be found.