There was a thread fairly recently where everyone submitted their thoughts on various on line retailers and, notably, ebay shops. Would be worth a search to find it.
eBay is a pretty good way to go, too. Just make sure you buy from a seller with a very high feedback rating. Some of the better Hong Kong sellers have 10k+ feedbacks. They must be doing something right.
Try some of these, see if they stock Tamron, would be interested to know how you get on with this as I’ve been having my eye on a purchase for a while and this lens peaked my interest too….