If you have 3 or more Gym Badges, you will be able to purchase them at "Delibird Presents" which are in each towns. 1 is 3,000 Pokedollars. Other than the 4 types of Stones, 2 types of Apples, and 4 types of honey, there will not be any other Evolution items.
Location Of Delibird Presents
★ Locations of the Delibird Presents
Picked Up By Red Glowing Poke Balls
On the field, there are red glowing Poke Balls. When you pick them up, there is a possibility they are Evolution items, so try picking them up to see.
The Sparkling Dropping Can Be Items As Well
When walking in the field, there are Sparkling items that shine. When you go near them and press A, you can pick them up and they can be Evolution Stones or Evolution Items.
Train Pokemon With Ability Pickup
If you train a Pokemon that has the Ability Pickup, after battling, there is a chance you can pick up Evolution Stones. It is a very low chance, but if you have a Pokemon with this ability, it is recommended to train.