looking for business sponsorship or donations

hi there,

i am a student intending on going to africa for three months to volunteer with aids sufferers in a medical centre, with street children and in schools working with the missionarys out there. i was wanting to write a letter to send to businesses asking them if they would be willing to either sponsor me or donate something which i can raffle off to raise money for the trip and the projects. i also thought to ask them to donate toys and clothes etc that i can take over or donate money with which i could buy stuff over there thus supporting their economy.

Could someone please help me word a letter which would get all of these points across in a constructive way.

thank you