Usually customer is interested to ship the components to us from outside of China intead of we purchasing that.But please note that normally China custom will charge extra duty taxes as below approximately:
ICs: 13% depending on the unit cost
LED, connectors.resistors and capacitors: 30%-50% extra taxesThe long lead time on the custom clearance process.
The necessary 3C (China Compulsory Certification) cerification for switches.
So, please double consider the whole cost of components by you is econmic or not than that if we provide the whole of components to your PCB assembly.