A lot of the music you describe (Deep Purple, Zeppelin) were prohibited by the Soviet state music stores. However there was a thriving black market within these stores and throughout the USSR during the 1960s and 70s. Employing used x-ray film to create DIY "rock on bones" records or reel-to-reel tape, many of the Western rock bands of the 60s and 70s found there way into Soviet homes. A crucial source for this was the Western Ukraine, Poland, and the Baltic which had a more liberal cultural policy than the rest of the Eastern bloc. These areas had more foreign tourists who could provide recordings, greater access to media, and looser cultural censorship. One Lviv radio station, although monitored, had half-hour weekly program devoted to Western music. All of this combined to make them a bridgehead for both Soviet bootlegs and Soviet rock.

Ironically, the state tried to counteract the influence of rock through the acceptance of disco. Within Lviv and Kiev, local Komsomol supervised discos as this was a more politically neutral genre of music. The minders of Soviet music policy thought that the rock of the 1960s and 70s was a ploy undermine youthful revolutionary energy with promises of hedonistic excess.

Under Glasnost, greater foreign contact and the abandonment of strict censorship meant that there was a decline in bootlegs. But by that time, Soviet rock music had developed its own indigenous base from the earlier Brezhnev period.

sources

Risch, William Jay. The Ukrainian West Culture and the Fate of Empire in Soviet Lviv. Cambridge, Mass: Harvard University Press, 2011.

Yurchak, Alexei. Everything Was Forever, Until It Was No More: The Last Soviet Generation. Princeton, NJ: Princeton University Press, 2006.