If you can't find screws locally, one option is to use a forwarding company like MyUS.com and order from the US.
The way it works is, you sign up, they provide you with a MyUS.com shipping address (like a post office box), then you can order anything you want from US online vendors using your MyUS.com address, those vendors ship the orders to your MyUS.com address, and then MyUS.com ships the items to you.
Of course it's not cheap. I got a shipping quote on the MyUS.com website for shipping a 1 pound package from the US to Italy and the cost was $14 US.
If you go this route, I know of a few online US vendors who sell 6-32 torx screws. They are McMaster-carr.com and Boltdepot.com. I use both regularly. Unfortunately neither ships direct internationally.
Again, if you go this route, and since you don't have the original screw to measure, you might want to order different lengths of the same screw so you get the best fit. If you start a new thread and post a request, someone with the same knife might be able to tell you the length of the screw (the threaded portion), and the diameter of the screw head, which could be important if the head is supposed to fit into a countersunk recess in the handle.
Boltdepot sells stainless steel pan head 6-32 torx (star drive) screws listed under the title "Machine Screws", at first the site only shows a philips head but if you click on it then you see the other head options. Boltdepot has a "no minimum purchase" policy so you don't have to buy a pack of a hundred screws to get just one or two. Their 6-32 torx screws are T15.
McMaster sells stainless steel button head 6-32 torx screws, but their T10 screws come in packs of 100, however they also sell higher strength 6-32 stainless steel screws individually that are T15.
