My friend from back home went to BKSP as a field hockey player. They normally get players by recommendation. I have not heard of BKSP going around the country scouting for talent. Students are enrolled in to the institute after class 6 beginning of class 7, approximate age about 12-13.
There are few BKSP around the country. But the one one in Savar is the first one.
This are few things I know. I will do some digging.
I love Bangladesh cricket and that's why I found BanglaCricket.com