A Chrono Trigger manga centering on the characters featured in the OAV (a Nu and Kilwala) and featuring others was published in V-Jump in the years immediately after Chrono Trigger's release. Bonus pages for the next chapter regularly appeared, including one depicting a 3D model of Robo. It was collected as a tankobon here, but is apparently out of print. Fortunately, an enterprising Chrono fan has scanned the entire thing:
- V-Jump Chrono Trigger Nuumamonja Manga (ZIP, ~247 MB)
It needs to be translated and scanlated, if anyone's up for the job. It has an entry on Material Requiring Translation. The Next Gate sequences were not included in the tankobon and still need to be scanned; post in this thread.
Thanks to Angerona, Rio Rock