Pascal,
Welcome to the carbine forum. We have members from all around the world who visit out forum.
As for your question.
Are you meaning an original GI rear sight tool, or an aftermarket version? The reason I ask is there would be a considerable price difference between the two.
We have a classified section up it the tool bar. There you can see what others are offering for sale/trade. You can also put in a WTB (want to buy) post, asking for an item.
Sometimes I've seen originals on Ebay.
There are also venders that sell original, and aftermarket tools. Here is an aftermarket one I saw M1 Carbine Rear Sight Install and Removal Tool M1 M 1 | eBay
I don't believe there is an issue sending a tool to Belgium. But you might want to check with your local area to find out.
I hope that is of some help.
Jim