The official HJC motorcycle helmet distributor/dealer for Bangkok/Thailand is Paddock in Bangkok.
You can contact Khun Tidarat Kerdphol at 169/84 Ratchada Pisek Road, Din Dang, Bangkok 10400, we have no idea if they have the HJC RPHA10 available in solid black, but you can call them at 02-6927000 until 5.
I have read the article about the HJC RPHA10 Motorcycle helmet.
Where can I buy one in BKK? I'm looking for a solid black.