A collection of resources
1. Faith and the reasons for unbelief by St Varlaam Ryashentsev
https://azbyka.ru/otechnik/Varlaam_Rjashentsev/vera-i-prichiny-neverija/
2. Mystical proof for the Existence of God by St Theophan of Poltava
https://azbyka.ru/otechnik/Feofan_Bystrov/misticheskoe-dokazatelstvo-bytija-bozhija/
3. Dialogues by St Valentine Sventitsky
https://azbyka.ru/otechnik/Valentin_Sventsitskij/dialogi/
4. Belief, unbelief and doubt by Metropolitan Veniamin Fedchenkov
https://azbyka.ru/otechnik/Veniamin_Fedchenkov/o-vere-neverii-i-somnenii/
5. The Sunflower, or conformity with the Divine will by St Ioann Maximovitch of Tobolsk
https://azbyka.ru/otechnik/Ioann_Tobolskij/iliotropion/
6. Leibniz's doctrine of the origin and essence of evil by St Joseph of Petrograd
https://azbyka.ru/otechnik/Iosif_Petrovyh/svjashhennomuchenik-iosif-mitropolit-petrogradskij-zhizneopisanie-i-trudy/4_4
To translate the sites into your preferred language use google translator.