The answer is pretty much no. Very little is actually known about the Zunbils, and almost everything we know of their religion is guesswork -- if you go back through the literature you find broad statements like "the origins and nature of this cult are highly obscure, except that it was clearly not Buddhist or Zoroastrian" and the Zunbils are a "series of enigmatic rulers known only by their titles". The identification of Zun with a sun god is itself only conjectural, despite what Crusader Kings II may have you believe. It derives originally from conclusions by Josef Marquart early in the 20th century that have later been shown to be suspect. Giuseppe Tucci has more recently argued that Zun was in fact a local cult of the Hindu god Shiva. We don't even know for certain whether "Zun" is the correct word: it could have been "Zur" or "Zor" or "Zal". In these circumstances of total uncertainty it's more or less impossible for anyone today to legitimately claim to be a follower of the Zunbil religion.