Paula Kirby, who once lived in the DDR, tweeted this photo of Trabants lined up on a dock for export: https://twitter.com/PaulaSKirby/status/724281792266522625
She doesn't know where else they were sold, though. Film footage from the USSR and other Warsaw Pact countries show plenty of Ladas and Skodas (and even the occasional VW or Volvo) but never Trabants. I'm curious about where else they wound up.
They were sold in Finland during sixties, and were the cheapest car you could get. Due to some trade political quirks and foreign currency regulation, you could buy a Trabbi that cost 4300 Fim, but not a Fiat 500 that cost 200 Fim more or a VW Beetle that cost 6000 Fim. When the regulation ended, so the sales of Trabants spiralled down. 1969 was probably the last year they were sold in Finland, and the number of Trabants in Finnish car registry was around 2800 then.
They were also exported to Hungary, Czechoslovakia, Poland, Bulgaria, Romania, and Yugoslavia