Do you need this as a one off for a concept or in volume.
Volume is easy because it can be made to order. 3000 min would see the tooling costs covered.
If it is for a concept then I would say, cut and attach an existing eject base to the one you need.
I have not seen what you are looking for on any website, but I am sure that it probably exists somewhere.
The main thing is to locate manufacturers rather than trading companies, especially in China, if you can get to speak to the actual manufacturer it is mostly quite easy to work any problem out.
However, my experience is that the majority of trading companies will swear that they are the manufacturer.
We have an employee based in China and his full time job is visiting companies in China just for this reason. To check them out.