Get the local climbing guidebook from Refugio Tisá, HUDY Hřensko possibly also from the local camp. Two options available:
Průvodce Ostrov: standard czech text guide, 2021, ~19€, uses traditional Ostrov grading system
Geoquest Kletterführer Ostrov: TOPO guide in German and English, 2020, ~40€, uses saxon grading system in line with Bielatal