@Jabbok Farms - They do commitment-free cash-on-delivery orders. You even get to pick exactly what you want in your box... they have over 100 things to choose from =)
Further more, if you want consistent supplies of produce year round you, can rent your own Ancient Food Garden at their farm, have them plant it according to your request, and whenever you want some of YOUR OWN produce they harvest and deliver it straight to your doorstep according to your request.
They take part in a few markets... the largest organic farmer's market by far is the Nour Al-Barakah market in a park in Al-Rabiyah... It takes place every Saturday from 10am to 3pm. Many different organic farmers and merchants display there.