Frame and/or fork damage is the most likely cause of the problem. If you could show some pictures of the bike, taken square on from the drive and the non-drive sides, that would be a help...


This not quite square shot shows the damage to the fork...


Pictures of the head tube junctions with the top and down tubes would also prove helpful. Look for cracks in the paint, a sure indicator of damage to the geometry of the frame and/or fork set. Damage to geometry == bent...


A picture, taken from the front of the bike and that clearly shows how the front wheel is centered in the fork will also prove useful. Look to see if the rim/tire splits the distance from the fork blades evenly...


One last thing could be a too tight headset and, worse yet, a too tight headset with damaged races, causing head set indexing, That can cause a bike to pull one way or the other.

Hope that is helpful.