Budew evolves at max happiness in the daytime. To get him at max happiness feed it poffins it likes. There is a poffin house in Hearthome City. Also give it massages. The massage girl is in a house in Vielstone city.
Ev berries can be obtained from a berry scientist in Pastoria city. Use a poketch up which you can get from the berry master's house just outside of hearthome city.
Here is a list of berries and what they do :)
Hope I helped :)