Here is the full list of all 12 Rock Band Country Track Pack achievements worth 250 gamerscore.
Full band clears "Free & Easy" with 100% notes hit on any difficulty
Score 10 million total points across all songs in Band Tour
Finish Band Tour mode on any difficulty
Hit all hammer-on notes in "Satellite Radio"
Hit 100% of the kick drum notes for any song on Expert
Get a 200 note streak playing Drums
Complete Solo Tour on Expert with any instrument
Complete Solo Tour on any difficulty with any instrument
Earn 75 stars across all songs in Solo or Band Tour
Beat "Suds in the Bucket" on Expert Vocals
Every band member scores over 90% of notes hit in "The Gambler"
Band members activate Overdrive a total of 10 times in a single song