Where can I buy a Wi-Fi antenna screw set?

After a recent service of my iPhone 4, the WiFi reception has deteriorated. Having checked the iPhone at another service center, I came to find out that they did not replace all the screws and I am also not convinced that the other screws are in the right place with the correct length.

Does anybody know where one can order a complete set of screws for the WiFi antenna? I am looking for the complete set, i.e. 1 x 2.3 mm, 2 x 1.6 mm, 1 x 1.4 mm and 1 x 4.8 mm.

Thanks in advance

J.

PS: Unfortunately we do not have an official Apple Shop/Service Center where I live.