Hi. I will try to did up some info on the original manufacturer of the Mobicel device's in hope to pull out their alphanumeric project names or model numbers. In that way, finding their stock ROMs should be simple. In the mean time, try emailing Mobicel requesting a ROM for the Mobicel Retro by completing and submitting the form here http://mobicell.co.za/contact/ and see if they may not be considerate and mail you a copy.
EDIT: The model's firmware is not readily available sadly. Do see the answer here http://satechhelp.co.za/1225/Mobicel-Retro-Privacy-Protection-Password-Which to learn of your options.