If I'm getting this right it is/was customary to utter a poem shortly after realizing enlightenment. Are these verses and/or maybe stories and accounts surrounding these beings collected somewhere?
Yes. For the Theravada tradition's stories of the elder monks and nuns, please see the following books of the Khuddaka Nikaya (the minor collection):
- Theragatha (Verses of the Elder Monks) or here
- Therigatha (Verses of the Elder Nuns) or here
- Thera Apadana (Past Life Legends of the Elder Monks)
- Theri Apadana (Past Life Legends of the Elder Nuns)
For e.g. you can read the story of Sunita the Outcaste who became an arhat elder.