I have many physical books of various Eastern European and Slavic tales in my childhood home, but nothing in English or in electronic form.. Anyway, Slavic and Eastern European fairy tales are not very different from other European nations' tales and have much in common (South Europe might be a little different, but I'm not an expert to comment much) to the extend that sometimes only character names differ (or animal type). You might try Grimm's Fairy Tales[1] if haven't read yet, but aim for original/older edition[2] as originally it was quite violent but softened increasingly over time.
1. https://en.wikipedia.org/wiki/Grimms'_Fairy_Tales
2. https://www.cs.cmu.edu/~spok/grimmtmp/