A Selmer should fit your mouthpieceI have one which is 33mm above and 35mm below when expanded (your mouthpiece, I suppose, would be conical)
So It should tighten well around your mouthpiece.
You should be able to buy this new for not too much money from Thomann for example. I am afraid that sending in a parcel (even small) it from the NL would cost more in postage than it would be making sense to you and the only other practical way is to open the ligature and flatten it onto a piece of carton to send it in an envelope with normal postage, when your receive it, then you make it round again around your mouthpiece.