I don't believe there has been any confirmation of weapons sent to Ukraine ending up on the black market or has there?
Ukraine has also arrested a number of Ukrainians in known smuggling rings selling captured weapons on the black market [1].
[0] https://news.sky.com/story/russia-gave-eur140m-and-captured-...
[1] https://www.standard.co.uk/news/world/ukraine-war-weapons-bl...
Im not seeing any sources saying that Russia is giving Iran hundreds of anti tank weapons? or guided artillery munitions?.