it may differ according to their need and shortage of staff...
but according to MBL new letters which is available on their sites you can google it. according to letters Karachi, Islamabad and Lahore training centers have capacity of 30 to 40 candidates Faisalabad 25 to 30 and Multan 20 to 25 (near about) but according to some seniors and MBL employees 20-25 but in big regions 30-35 almost.
(an idea according to different informations)

and let see and hope for the best...