Always had an interest in both the Falklands conflict and the troubles. Since the IRA and the Argentineans were both against Britain I’m sure the IRA supported the Argentineans, but I’ve never heard about it.
While the IRA in theory would have supported anything that weakened the British Empire, it's important to note that the R in IRA stands for Republican. The Argentine government at that time was ruled by a military dictatorship, and so the IRA were not too keen to support them.
There is also the issue that the IRA were much more invested in actually attacking London and Britain to economically harm them and Kill Margaret Thatcher. To my knowledge they had no official stance on the Falklands war, at most referring to it as the Malvinas as some Irish do to spite the British.
Source: Am Irish, have studied this period in University, particularly the IRA during Thatcher and the Falklands conflict.