Russia.
Sources indicate Ukraine may have received Grad munitions through Serbia. They were allegedly sourced by a Canadian company through Turkey into Slovakia and then Ukraine.
Сербские "Грады", предположительно, уже на передовой. На стороне ВСУ, конечно. Опознавательный признак - краска, и покрытие блока стабилизаторов. Дальность, к слову, почти вдвое больше, чем у советских "Градов" (40 км против 20,4 км).
t.me
vk.com
I was sort of following this at the time, and the controversy over it in the Serbian press. I just now looked for news in English, as I doubt many here read Serbo-Croat*, but not a whole lot to be found. Here's one claiming that apparently the very colorful figure Slobodan Tešić was involved:
Serbia has not officially exported weapons to Ukraine since the beginning of the armed conflict in Donbas, and later the Russian-Ukrainian war. Nevertheless, the Russian media report that the rockets from the Krušik arms factory, through intermediaries, ended in the hands of the Ukrainian army...
www.serbianmonitor.com
The Serbian defence minister recently denied Serbia had agreed to supply arms to Ukraine as claimed in the leaked documents now very much in the news (and the article claims a US company was involved, but only cites a Russian source for this, and again, claims Tešić involved):
Defence Minister denies claims made in alleged leaked Pentagon document that Serbia has agreed to supply arms to Kyiv, saying: 'We have denied those falsehoods more than ten times'.
balkaninsight.com
According to the Toronto Star, Serbian Foreign Minister Ivica Dačić said "If private companies buy weapons in third states’ markets and then sell them to other companies in other countries, that is not a question for Serbia, that is international trade."
BELGRADE, Serbia (AP) — Serbia on Friday denied it has exported arms to Ukraine after Moscow demanded to know if its Balkan ally delivered thousands of rockets for Ukraine’s fight against Russia’s invasion.
www.thestar.com
As for President Vučić, he waffled on the issue, first claiming:
On 5 March, Serbian President Aleksandar Vučić refuted the statements on supply of Serbian ammunition to Ukraine or Russia. Source: Vučić at the UN conference in Qatar, reports European Pravda citing Danas Details: According to Vučić, not a single item of Serbian weapons or ammunition has been...
www.yahoo.com
And more recently repeating Dačić's line. I have my own educated guess about how this might have gone down, but will keep it to myself as I can find no supporting links for it. Anyone familiar with the Balkans and how things are done there and with Vučić's predicament can correctly surmise what it is.
Anyway, there has been controversy over the legality of Grads, and when and where they might legally be used, including arguments in the Hague. HRW has cited Ukraine forces (among others) for using them illegally in the past. Of course Russia uses them, too. The arguments are interesting, but probably belong on another thread. I am not sure which one.
Meanwhile, we have something of a curiosity here in the US. It seems a Russian T-90 captured by Ukraine has turned up at a Louisiana truck stop:
A truck carrying what’s believed to be a captured Russian tank was left stranded for two days at a truck stop in Roanoke, La.
www.ksla.com
The T-90 tank is thought to have been captured last September by the 92nd Separate Mechanised Brigade, after being used in Kharkiv
www.telegraph.co.uk
This might turn out to be a fun story. I've always said Wars Can Be So Strange, and, truly, strange things really do happen in war.
*I refuse to split Serbo-Croat into the ridiculous, political and unscientific divisions "Bosnian", "Croatian", " Montenegran" and "Serbian". I am a stickler for such things, I suppose. The vast majority not only speak the same language, they speak the same standard dialect (Štokavian).
Edited to remove a small unimportant personal bit.