Try this website
Samyang Lens_çRî^_Photoman
They have two shops in HK. One in Wanchai (灣仔
and the other in ShamShuiPo (深水埗
Address:
HK Island: 香港灣仔軒尼詩道298號298商場UG層121-122鋪 Tel: 28922226
Kowloon: 九龍深水埗深之都1樓 139-141 鋪- 近深水埗地鐵站 Tel:35686223
Visit their website before arrive in HK. Their website price is usually lower than the one in the shop. You can always quote their website price to get the lower price.
Bought my 14mm F/2.8 there.
You can also try Sim City in Mongkok. There are shops that carry Samyang lenses as well.