Where do I find a - preferably official - 3.5 update for the Sha'ir from Al Qadim (the boxed setting for AD&D 2nd ed.)?
(Not about to DM the setting just got curious about the d20 adaptation of the game mechanics.)
While I couldn't find exactly what you were looking for, I did find some resources that might set you down the right path:
Again, nothing exactly like what you requested, but hopefully that might give you enough ground to convert the class from 2e, from 3e, or from Pathfinder to meet your 3.5e needs, and with any luck those 3.5e links might start working again.
An official d20 version of the Sha'ir was presented in Dragon 315 (to the extent that Dragon is official). It's quite close to the AD&D Sha'ir in flavor and relatively close in abilities.