You were totally on the right track with Foundry's Darkest Africa line. The Ruga-Ruga are not the only figures which might meet your needs. In the Azande line there is a pack of guards which is musket armed. The Baluchis are also really good, along with the Zanzibaris. Some of the tribal figures would be fine to throw in also, since that fits in with the exotic nature of your project. In fact, the African maiden warriors would really spice things up!
You might also consider the line of Dixon Ottomans. No pics I can point you to, but I just ordered a lot of these because the US distributor in Nashville, Tennessee is having a closeout sale. I hope some of them turn out to be useful as Arab pirates.
Copplestone has a cool pack of Azande musketmen that must have been sculpted after he left Foundry. Those would add to the exotic look.
Reaper has a few Arabian nights type characters, male and female, that would be good. Although the Reapers are expensive, there are only a half dozen or so that you might want to buy, and they are not too much more pricey than the Foundry, Dixon, and Copplestone figures.
In fact, you will have to have someone for your Madagascar pirates to fight. And the Arabs, Zanzibari, and Baluchi figures mentioned above and by previous posts would be excellent for manning an opposing ship.
Last but best, the outrageously expensive Hasselfree line has three black women Harem guards that are just to die for. If you want a really exotic look, these are a must have. These three figures are some of the best I've ever seen.