Check out the product catalogue for NMK (national museams of kenya). They give you info on seating capacity,available times costs and 8 different venues for hire.
Came across their site once and - given the pics they've posted - thought their venues seemed ideal.
You can also consider going for an 'out of Africa' theme for your party and rent out the Karen Blixen Museum grounds... Check out their site for further info.
All the best.
The economy changes.....good investment principles don't.
Généralement, les gens qui savant peu parlent becoup, et les gens qui savant beaucoup parlent peu.
- Rousseau.