Waleed,
Why not use some resources that are currently employed by film production or theater groups in Riyadh? The process for print/still casting is essentially the same as film or theater. Here is a link to Mandy.com localized for Saudi Arabia.
http://www.mandy.com/4/saud.cfm
I'm sure that a Google search as well as your own personal contacts will point you in the right direction.
I hired models and actors through Mandy.com in London earlier this year and I was pleased with both quality and quantity of talent.
You can make a specific casting call for each individual job rather than trying to establish a large database. Most actors and models already have a headshot that they can e-mail or they can send a link to their online portfolios. Once you have made an initial select, you can then invite the best candidates to your studio for a headshot.