During the Comiket 88 event this year, manga artist Takeshi Nogami (Girls und Panzer) distributed a fake magazine containing two The Third Girls Aerial Squad (Dai San Hiko Shoujo-tai) manga chapters, and it is now available in several establishments in Akihabara. The Third Girls Aerial Squad is a manga and anime series that appears within the Shirobako TV anime.
An OVA episode based on The Third Girls Aerial Squad shipped with the seventh Blu-ray and DVD volume of Shirobako in July. An OVA based on another fictional work featured in Shirobako, “Exodus!,” was included in the third DVD and Blu-ray set.
Source: Akiba Blog