Well...I'm surprised to see so many Cadillac cars in a country like Poland...I know that Cadillac was officially sold in Russia (maybe no more) and I can imagine the difficulty to get spare parts. Congratulation!
'in a country like Poland' -
. Well, this is a problem You mentioned regarding Your former employers - no clue about European markets. Most Germans for example treat Eastern countries as underdogs but they have always seen business opportunity here and kept on investing in their infrastructure. Thanks to it nowadays You'll find in bigger cities more 3,5-series BMWs than Octavias and more X3/X5s than Kodiaqs or Opel Suvs. New ones (mostly leased) used (mostly wrecked ones imported from Germany and Switzerland). There's a great variety of choices and access to parts, financing and service. And GM ? Opening one single sales/service outlet and keeping it has always been a mission impossible. Somehow Chrysler/Jeep managed to have distribution network from early 90's and keep it. The dealer in Warsaw still exists, they were the first in the country to have a parking lot on the roof - later many copied them including new Mercedes dealer. And no one will tell me the products they offered at beginning (thirsty Jeeps, 300C, Sebring) were suitable for Europe. Nowadays they expanded their portfolio do Dodge and RAM. So if I wanted I could lease a Durango or Challenger 5 km from me. Try to do it with a Corvette or Cadillac.
And here's a picture of the first Chrysler dealer in Poland from 1929. Most of the American manufacturers had their outlets in interwar period. Sadly after the war broke out only Chrysler made a come back. The building still exists today as one of a few that survived heavy bombings. I can show You it when You visit Warsaw.
GM once tried to distribute parts for Chevy/Cadillac through Opel dealers. It failed miserably of course as no one wanted to pay their crazy-high comissions. Especially after internet sales became so popular, most of the smaller parts are very easy to get and sometimes websites as RockAuto are able to ship them within 4-5 working days. The problems appear when sb. wants to import big body parts. This is very expensive and when I owned a Firebird I had problems with finding a company that organises shipping of hood to Poland.
As for Russia, I don't know why You even mention this country in one sentence. It's a completely different world. In fact GM never neglected it as much as Europe. And now in theory they closed their business. On BBC I saw a report about 120 new Escalades stuck in a port in Belgium that were supposed to go to Russia. But visit accounts of Russian rich instagramers and You will see how their brag about their fresh-delivered new Caddies. This is reality. I know sb. who works at Mclaren/Aston/Rolls dealer and somehow they sell to Russia without a problem.