Each weapon station needs to be defined as a subcomponent of the fuselage:
SystemName[010]=SparrowStation1
SystemName[011]=SparrowStation2
SystemName[012]=SparrowStation3
SystemName[013]=SparrowStation4
The numbers need to be sequential, and the system name should correspond to the name, in brackets, of the weapon station you added, for example:
[sparrowStation1]
SystemType=WEAPON_STATION
StationID=6
StationGroupID=4
StationType=SEMI_RECESSED
AttachmentPosition=-0.501,5.07,-0.84
AttachmentAngles=2.0,0.0,2.0
MissileRollAngle=45.0
EjectVelocity=0.0,0.0,-2.0
LoadLimit=231.5
AllowedWeaponClass=SAHM
AttachmentType=NATO,USAF
MinExtentPosition=
MaxExtentPosition=
[sparrowStation2]
SystemType=WEAPON_STATION
StationID=7
StationGroupID=4
StationType=SEMI_RECESSED
AttachmentPosition=0.501,5.07,-0.84
AttachmentAngles=-2.0,0.0,-2.0
MissileRollAngle=45.0
EjectVelocity=0.0,0.0,-2.0
LoadLimit=231.5
AllowedWeaponClass=SAHM
AttachmentType=NATO,USAF
MinExtentPosition=
MaxExtentPosition=
[sparrowStation3]
SystemType=WEAPON_STATION
StationID=8
StationGroupID=4
StationType=SEMI_RECESSED
AttachmentPosition=-1.08,-0.65,-0.87
AttachmentAngles=0.0,2.0,5.0
MissileRollAngle=45.0
EjectVelocity=0.0,0.0,-2.0
LoadLimit=231.5
AllowedWeaponClass=SAHM
AttachmentType=NATO,USAF
MinExtentPosition=
MaxExtentPosition=
[sparrowStation4]
SystemType=WEAPON_STATION
StationID=9
StationGroupID=4
StationType=SEMI_RECESSED
AttachmentPosition=1.08,-0.65,-0.87
AttachmentAngles=0.0,2.0,-5.0
MissileRollAngle=45.0
EjectVelocity=0.0,0.0,-2.0
LoadLimit=231.5
AllowedWeaponClass=SAHM
AttachmentType=NATO,USAF
MinExtentPosition=
MaxExtentPosition=