Get the local climbing guidebook from Refugio Tisá, HUDY Hřensko possibly also from the local camp. Two options available:
Geoquest Kletterführer Ostrov: TOPO guide in German and English, 2020, ~40€, uses standardized saxon grading system wherever the grade is known (marked with "RP").
Průvodce Ostrov: standard czech text guide, 2021, ~19€. Pay special attention as it uses the traditional JPK grading system! (see grading in description)