You may also look for Polish-grown Saazer.
Tastewise, it's said to be even closer to the canonical Nowotomyski.
It's rarely advertised directly, but a good deal of the globally sold Saazer is actually grown not in Czechia but in Poland. A slightly lower price for an otherwise normal Saazer might be a hint. Then you ask the seller about the batch origin and if you're lucky, he's aware it's from Poland.
Don't buy Marynka, even if you find it! Although it's Polish, it's essentially a Brewer Gold's progeny, so not even close to the Saazer-like Nowotomyski required for Grodziskie.