Darkness said:Discern location is 8th level and has a very, very specific effect. It's blocked by another 8th-level spell (i.e., mind blank).
Also, it's in the nature of D&D that defense often needs to be somewhat less specific than offense. Otherwise, you'd need way too many defenses to get by.
It could be argued that True Seeing is a "defense". It at least shades apon the catagory of defensive spell. That being said I too find it a bit disconcerting that a 5th level spell, even at 250gp a pop, can over come all that it can, completely negating an entire school of spells. At leat the true seeing goggles cost 70K takes up a large chunk of equipment resources until the mid-teen levels or higher, unless it is a common property party item ( "My turn with the shared brain today!"

I suppose an antimagic field interposing between the caster and the polymorphed target might block the true seeing. Certainly containing the caster within the Antimagic field would. But that would present some logistic difficulties.
P.S. Your character could fall back on the mundane for disguse, assuming you aren't trying to radically alter your appearance.