"I'm sorry, but I can't find the request you sent for information for your supervisor's mid-year evaluation. Could you resend that request so I know what to give you?"

Seriously, what's wrong with that? "I'm sorry, but..." is a perfectly good phrase if you use it when you really ARE sorry about what you're about to say,
That is true.( but) It's all about the disclaimer that might follow the "...but". This is turning into a huge semantics discussion

I'm sorry I didn't pick up any beer, but you drink too much anyway.
I'm sorry I didn't come to dinner, but your friends are a bunch of jerks.
I'm sorry I cheated on you, but I'm not getting what I need.

etc.