Bugger! That's a worn bolt head... Has the roller been scored/flattened as well?
Probably immaterial actually. First call, see if one of the NI or IoM members can recommend a good old fashioned pistol smith. You want someone whose been around a while, it's surprising the parts they have in drawers. On top of which, they'll also have the contacts.
Your massive problem is going to be getting the said part to you. Your going to need a variation for it. Then your going to need someone who can import it....
A quick trawl has shown a couple of complete bolt heads for sale in the US. Pointless for you, but they run at $350 plus! There are a few places in Europe that break guns a la Numrich, and you really could do with a German firm as they still do live their HKs! Drop this one an email;
http://www.augustine-waffenteile.de/shop/
Worst case scenario is that it's dead. You may be able to spend a wee bit and have it deactivated in order to recoup some of your costs. I can't imagine you paid the £335 i paid for mine in 1990....
Sorry to hear this.
In 1978 I was told by my grand dad that the secret to rifle accuracy is, a quality bullet, fired down a quality barrel..... How has that changed?
Guns dont kill people. Dads with pretty Daughters do...!