Kirito and Sinon's outfit will be available in GE2RB while Julius' clothing for Kirito and Alisa's clothing for Asuna clothing will be available in SAO:LS.
The link for the news article in Siliconera is here.
In the localised versions (english subs) of SAO: Lost song the DLC is pre installed and can be found in the cabinet where you change your armor under equipment. Select "GE Collab. Outfit"