In short, source, shortlist and sample from 3 to 6 factories.
The long version . . . . .
1. Contact as many stationery suppliers that you feel are able to do what is required.
2. Shortlist to 10 and disclose your requirements, gauge their response, communication, understanding your exact requirements. Ask for quotes, delivery times, minimum order quantities and sample availability.
3. Shortlist to the best 3 suppliers and sample with each.
4. Select the best product, based on quality, not price.
5. Carry out due diligence on the supplier and start the order process.
Branding, packaging and packing are all important issues you need to clarify, check and confirm.
If it's your first time ordering from a China supplier, have someone 'hold your hand' to help through the hurdles of working with a China factory.
For all orders, I advise a contract, quality control and arrange your own shipping to your door.
If you haven't found a suitable supplier yet in UK, you can do worse than trying China.
Keep your options open, until you are happy with any samples you source.
If you need any further advice on sourcing or purchasing from China, feel free to ask.