Below you can find the direct links to Download AppleTV Firmware Files for every released firmware version.
Latest:
11.2.6 (ATV 4): AppleTV5,3_11.2.6_15K600_Restore.ipsw
7.2.1 (ATV 3 New)*:AppleTV3,2_8.4.1_12H523_Restore.ipsw
7.2.1 (ATV 3)*:AppleTV3,1_8.4.1_12H523_Restore.ipsw
6.2.1 (ATV 2):AppleTV2,1_6.2.1_11D258_Restore.ipsw
Please go to next page for Full List and Version Comments.