Dear Petra,
The book, A Critical Appraisal of Ayurvedic Material in Buddhist Literature with Special Reference to Tripitaka, by Jyotir Mitra (Varanasi, 1985), refers to kucchi-roga on p. 244, merely calling it "abdominal disorders." However, it gives references: Jataka I.243, and Anguttaranikaya X.6.60. I do not have the Pali commentaries on these texts, but they might possibly gloss kucchiroga.
This book on p. 233 also refers to a list of 34 rogas at Niddesa I.18 that includes kucchiroga. Again, the commentary might be worth checking.