Hello!
I think I can give you some info here - I started modelling in Poland in 1986 - that gives me three years experience behind the iron curtain, plus some tales I have heard from my older friends.
As for the western kits - those were only available when somebody went abroad and bought them personally, or they were sometimes sent as gifts for those for those fortunate enough to have relatives abroad. The economic differences between us and the world made those kits very expensive - a western kit could cost you sums comparable to a monthly wage of a factory worker - that's how I have heard it. Consequently a model kit was equal for many people with tons of money, and that notion lived very long. Once in the late nineties I have put some empty boxes from the kits I have built in a cellar in our block - and somebody promptly burglarized that cellar hoping that the boxes are full...
Kits that were sometimes available in stores - and then you had to wait in a long line to get them - were manufactured locally. In Poland those were mainly "Plastyk Pruszkow" kits - Jak-1, Il-2, RWD-5, PZL-37 Los, LWS Czapla were most popular. Lucky paople could get their hands on Czech kits - Kovozavody Projestov = Kopro = KP. They had some MiGs, some Avias and Aeros, Jak-23, some helicopters - that was really a treat after building several Los... Then there were the East German VEB Plasticart kits - they had some models that were just gigantic in comparison with "our" models, all those airliners in wild scales, they had a Be-6 flying boat, Soviet Bombers and stuff like that.
Castelnuovo - the helicopter you mean was the Jak-24. That was a funny rig!
And there were the soviet kits - copies of the Frog kits, those were had to be brought by people travelling to the Soviet Union, they weren't exported much, sold under different brands and often without box or decals, just packed in a plastic bag with very basic instructions. But the subjects could be very interesting - planes like DH Vampire or HS Buccaneer, and label "Frontline fighter" or "Fighter-Bomber" - and you were left to guess what it is. We wouldn't want to advertise for a capitalist, now would we, comrade?
But to get one of those plastic kits you would really have to save some nice amount of money and have many friends with connections to people who would go abroad - at least to the socialist countries. So many times a young modeller was left to "Maly Modelarz" paper models - or you could go to a local modelling club - there were many of them than - and they would help you carve something from wood, or build a flying or swimming model from scratch.
And then came 1989, the wall broke down and all hell was loose - you could buy almost everything, but you didn't have any money anymore... Those were the days!
Thanks for reading and have a nice day
Paweł