Compared to five years ago the market for many non-USA coins has changed a great deal. Then it was still possible to acquire most modern coinage at a relatively small mark-up over the issue price and often directly from a country's mint. Now due to incresed popularity of their coins, some countries only sell their coins through a distributorship who in turn sells the coins to dealers. The resulting premium to the collector can be substantial.
Where to buy older, rarer, modern Chinese coins? If I knew specifically what I wanted, I would solicit the services of ONE dealer who specializes in the coins you wish to acquire. Work out all the details of your arrangement before hand. Expect to pay 5 to 20 percent for the dealer's services. In many instances this will prove to be a bargain. Rare desirable coins are seldom found without a great deal of effort.