You can get everstone from wild Geodudes/Gravelers and one from Professor Elm if you show him Togepi.
In Pokemon crystal you'll have to get the numbers of a few trainers and occasionally they will offer stones:
Fire Stone: Schoolboy Alan, Route 36
Water Stone: Fisherman Tully, Rote 42
Thunder Stone: Lass Dana, Route 38
Leaf Stone: Pickniker Gina, Route 34
Hope I helped!