Hello,
Thank you for your question and visiting the Ask an Advisor site. Although your question is a bit out of our area, I can help think of some potential paths. I would start by recommending building connections with institutions who have ambulances. I think they would likely be the most informed about how the process of ambulance donation would work. I am not familiar with Ugandan systems, but perhaps there are emergency and other ambulance services there that may be able to help.
Good luck with your work! Thank you again for contacting us!
Charlie