How can I buy a wishpoint?

[Ungod]

Is there such a way?

[MaGoHi]

you can not buy a Wishpoint, you can only earn them by doing quests that offer them as reward or by solving some of the puzzles that you can find within the realm

[Demonic God]

Wishpoints are earned, not bought. Any attempt of trading/buying WP outright will lead to punishment and the removal of the foul WP.