This might sound insensitive but, right now is probably the best time to exporting animals from Sri Lanka, may it be purple-faced langur, tufted grey langur, toque macaque, loris, grizzled giant squirrels, or or even elephants and leopards. Quite frankly I think zoos should take this opportunity to be able to import some rarities that need exsitu breeding programmes asap.
@Kestrel According to the CITES trade database, at least 3 pure purple-faced langur were imported in 2011 from Great Britain, according to the post by @TeaLovingDave linked below, these most likely came from Cotswold Wildlife Park.