It's near impossible. Ask me how I know.
The major flash tunes are Cobb, GIAC and Dinan. Call or email a GIAC dealer in your area; they'll be able to run your VIN and tell you if your car is in their database. A dealer would be able to tell you if it's Dinan, and Cobb can also run your VIN.
It's likely an open source dyno tune, though, which you will likely never get to the bottom of if you can't get a hold of the previous owner.
2008 E90 335i // Black Everything // photos
COBB tuned / QTP e-cutouts / Helix FMIC / cp-e DCI / AWE BOVs / Black M6 wheels + Toyo Proxes
(and yes, I am a girl)