Here's an interesting pic of a Chinese flintlock blunderbuss, the barrel and stock are Chinese with an English flintlock mechanism:
Flintlock was never widespread in Qing China. They skipped right from matchlocks to percussion caps following the Opium War. When I visited the Taiping Rebellion museum in Nanjing I was surprised that all the firearms on display were converted to percussion caps (even a large Jingal).