If I want to add the psychic keyword to my wizard powers, the only thing I can come up with is to get heavy blades as an implement, and use a Githyanki Silver Sword. Are there any other ways to get it? In particular, a way that will allow me to take a superior implement?
The only other weapons that convert damage to psychic is the Mindiron Weapon (bow/crossbow only), and Sorrowsong Blade (Heavy Blade only). These come with an always on 1/2 damage psychic property. There are no implements that change the damage to psychic.
The better choice would be to take a healthy slate of psychic keyword powers. Wizards usually have a psychic choice or two at every level.
Talk to the DM and see if you can re-flavor your powers to be psychic.
There was an article on doing exactly that in Dungeon #394 Dec 2010:
It is also possible to change the damage type of powers or feats to better fit a character—with the Dungeon Master’s permission. For example, a disproportionate number of feats favor cold-using characters; changing those feats to another damage type should not automatically break the game. Such a change should not be made lightly, without considering the ramifications, and certainly not without consulting the DM.
The article also touches on modifying classes and races, an example given is a minotaur warlock turning its eldritch blast into and eldritch strike.