The Cold War was really just a side point to the Troubles(As the Irish call it). The only time there was any real direct involvement was when the Soviet Union supplied arms to the Official IRA through the KGB starting in 1972 - a KGB operation known as Operation SPLASH. The Communist Party of Ireland, which was Marxist-Leninist and within the Soviet sphere, acted as an intermediate. The whole thing was authorized by Yuri Andropov, who at the time was head of the KGB, not the President or General Secretary.

This relationship developed far enough that the OIRA eventually even established links with North Korea and Czechoslovakia in regards to acquiring arms and even military training.

The Soviets chose the Officials due to their Marxist tendencies, and they were much more pliable to manipulation - in the words of O'Riordan(Leader of the CPI) in regards to the IRA, "they unfailingly accept our advice”, though we can't really know if he was a reliable commentator.

In terms of the narrative of the conflict, class warfare and Communist/Socialist politics was definitely something that was a theme of the conflict. One of the leading Provisional IRA commanders, Brendan Hughes, was an ardent Socialist and believed he was fighting for a Socialist Republic, and you'll note that all the Republican parties in the North have a left-leaning tendency(For example, Sinn Féin, the political wing of the PIRA, was an advocate of Democratic Socialism), though the non-violent SDLP is less radical in this regard.

In regards to it tying into geopolitics as a motive - not really, no. The various derivatives of IRA throughout its existence aligned with virtually anybody that would support their cause, from the Germans in World War I, to the Soviets in the 20's, then to the Nazis during World War II, and so on.

Geopolitics as a factor only came into it insofar as aligning with those that opposed the British Empire/United Kingdom. It is undoubtedly the case that many members of all sections of the IRA during the Troubles had radically leftist tendencies, and should the conflict have swung in their favour, the geopolitical position of a Socialist Ireland could've been very pro-Moscow, but that wasn't really a part of the conversation, nor was it ever really seen as spreading the Socialist international revolution, but there were very strong tones of class struggle against what was seen to be a Protestant, Unionist Elite class.

The weapons themselves were of generally non-Soviet origin in order for there to be plausible deniability, and were used for a myriad of different things - including against other Republican paramilitaries such as the Provisional IRA or the Irish National Liberation Army(Which was also a very far left group).

In terms of sources, they're actually somewhat difficult to dig up. Most of what I just said there is from memory from my brief readings on the subject, but there has been leaked intelligence from Russia in the 90's that pretty much outlined the KGB's actions in Northern Ireland and the IRA's relationship with the Communist sphere.

Operation SPLASH and other related interactions with the Republican Paramilitaries during The Troubles is outlined in The Sword and the Shield: The Mitrokhin Archive and the Secret History of the KGB, a book written by Christopher Andrew(Co-Authored by Vasili Mitrokhin, who was a senior archivist for the Soviet Union foreign intelligence service).

Just to expand on the geopolitics segment of your question would the arms shipments and semtex that Colonel Gaddafi provided the Provisional IRA be of interest or are you solely interested in the funding by the USSR and other communist organisations?

/u/Cyridius did a great job answer the question. I would just like to add that I don't believe enough people understand the fundamentally different ideological background to the two sides of the conflict.