The one "near" Alexandra Hosptial is actually "in" the compound. It is just behind the bus stop. A small little valley to the right after u enter the small gate just behind the bus stop.
If you take MRT, alight at Queensway MRT station. Follow the instruction to AH -- take bus 195. Alight opposite the hospital, cross the overhead bridge ... right in front of u will the bus stop. walk another 10 steps or so, on your right, that is the gate. ;p