Many thanks, all, for the replies!
I did originally approach three gunsmiths to make this for me. The first one has a lathe that isn't fast enough, he could not make the pin and recommended I find someone with a high speed lathe (more than 4000 rpm in his opinion).
The second one can make the pin, but he wants the whole rifle sent in (which is an unnecessary expense to me because I have to pay £15 for Parcelforce to mail it out and then I have to pay an RFD a small fee to receive the rifle back, as it cannot be mailed back to me directly. On top of that, I don't want my red dot sight and magazines being mucked around with in transit or at the gunsmith. It is faster just to have the pin duplicated.
The third guy will make it on a CNC unit, but at unacceptable expense.
Now the question about the part itself.
It is from a semi-automatic .22 rifle, specifically a SIG-SAUER 522. SIG Arms in the USA will not send out parts to me here in the UK, and they won't send parts to the UK distributor either. So I'm pretty much stuck unless I have it made here in the UK or try to source one from a gunsmith in the US.
As many have said already, manufacturing or possessing the firing pin for this rifle is not the same as manufacturing or possessing pressure-bearing components or whole barrels and receivers for firearms. It is an unrestricted part entirely, the same as the hammer and the trigger.
Here is the gun:
[URL=http://s55.photobucket.com/user/Odd_Job/media/522-2014_zps3b0f2e18.jpg.html][IMG]http://i55.photobucket.com/albums/g154/Odd_Job/522-2014_zps3b0f2e18.jpg[/IMG][/URL]
It's on my Firearms Certificate (along with two other rifles).
The Firearms Enquiry Team can verify that my FAC is valid:
Tel: 0207 161 4750
[email protected]
6th Floor
Empress State Building
Empress Approach
London
SW6 1TR
I'll give whoever makes the pin my FAC number if they are still worried they are helping the next Carlos the jackal 