Basically what the title says. I've been trying to look through Wikipedia and other sources but to date have found no examples of USSR involvement in UN Peacekeeping efforts, either by supplying troops or material. If this is correct, any idea why they didn't? I would assume a major power with worldwide aspirations would want to project military strength through non-unilateral means (i.e. no proxy wars such as Vietnam, Korea or hot conflicts like Afghanistan) as a PR boost to their image around the world.
They never sent troops or police or materials. They did, occasionally, send observers, most notably in the 1973 Yom Kippur war, as part of the UNEF II mission. Their first involvement with actual troops and police was after the breakup of the USSR, when the Russian Federation sent about 1500 troops and 30 police with the UN Protection Force during the Yugoslav war in 1992.
The concept of "peacekeeping" so far as the UN is concerned is all about not taking sides. If there's a civil war, the UN doesn't say which side is right or wrong, they just ask both sides to resolve their differences through peaceful means. A UN peacekeeping force only goes in to enforce the peace in some delimited pre-agreed area. The idea is that civilians fleeing the war may find refuge in the safe zone enforced by UN troops. It doesn't always work out that way, but such is the intention.
This was not the Soviet Union's philosophy. For them, there was always a "right" side, and that was the side that Soviet leaders defined as "progressive". This usually corresponded to Marx and Engels' idea of proletarian internationalism, that the proletariat must act globally to fight capitalism. Practically, it meant the side sympathetic to socialism or communism, or the side opposing the west's "imperialism", which according to Marx was the end point of capitalism.
There's an essay by Alexander Sokolov entitled "Russian Peace-Keeping Forces in the Post-Soviet Era" which goes a bit into Soviet times as well, about why the USSR didn't care to participate in UN peacekeeping missions. It might be interesting to you. It's in a book called "Restructuring the Global Military Sector" which is mostly about post-Cold War politics but also contains by way of introduction how things came to be.