Not from U-N, this strap was from Hysek; ordered factory direct.
This was from Bell & Ross via my local sales lady Yolanda; buckle not included.
This was from Silberstein, buckle not included. I see the replacements on the left with leather lining came from Hirsch straps - you might contact them about the UN pieces you want -- maybe?
This from St Gallen/PuristsPro -- replacement courtesy of a gentleman.
Overall, I have not had very good luck with rubber straps!