From Reddit:
Italics are debuts of solos, duets, groups, and subunits but not collaborations. There's a lot happening during the summer, so I've probably missed a few so just post if anyone else is having a Korean/Japanese comeback too. (edit: There's also little to no chance of Girl's Day, Sistar, Girls' Generation AND APink promoting during the same month so those dates are pretty flexible)
1 June
• Big Bang- Single: A (Pop/Rap)
• Year 7 Class 1- Single: White Breeze (Pop)
2 June
• Namjoo and Sungjae- Single: Cube Project Photograph (Pop)
3 June
• Crown J- Single: LOLO (Hip-Hop)
• EXO- Repackage Album: Love Me Right (Pop)
• A-KOR BLACK- Mini Album: How We Do (Hip-Hop)
• Jang Jae In- Pre Release Single (Pop/Ballad)
4 June
• Lee Seung Gi- Album (Ballad)
• HIGH4- Single: Baby Boy (Pop)
5 June
• Boys' Republic- Single: Hello (Pop)
8 June
• Eun Ji Won (ex Sechs Kies member)- Album: What U Are (Pop)
9 June
• MBLAQ- Mini Album: Mirror (Pop)
• Melody Day- Single: Love Me (Ballad)
10 June
• GOT7- Japanese Single: Love Train (Pop)
Tentative June Releases
• Seo In Young (Pop)
• Jang Jae In- Album (Pop/Ballad)
• Nicole- Japanese Single (Pop)
• Tymee (Rap)
• Cheetah (Rap)
• Sistar- Album (Pop)
• Mamamoo- Mini Album (Pop)
• AOA Rap Subunit- Single (Pop/Rap)
• Teen Top- Mini Album (Pop)
• GFRIEND- Mini Album (Pop)
• Nine Muses (Pop)
• Girls' Day- Mini Album (Pop)
• APink (Pop)
• SPEED (Pop)
• BTL- Single (Pop)
• 4MEN- Mini Album (Pop/Ballad)
• Dasoni (Pop)
• 2PM- Album (Pop)
• Royal Pirates (Pop/Rock)
• Girls'Generation- Album (Pop)
Releases in the Near Future
1 July
• Big Bang- Single: D (Pop/Rap)
• Dongwoon (of B2ST)- Japanese Mini Album: Kimishika (Pop)
8 July
• Yunho (of TVXQ)- Japanese Mini Album: U Know Y (Pop)
22 July
• f(x)- Japanese Single: Pinocchio/Hot Summer (Pop)
• Crayon Pop- Japanese Single (Pop)
Tentative July Releases
• Hara (of KARA) (Pop)
• AOA (Pop)
• GOT7 (Pop)
• f(x) (Pop) (obvious july comeback)