OK, let's take a look onto your issue, what i will explain you can do it on the TMF MIG-29, i'll be using the MIG-21: go to your main game directory, let's use by instance Wings Over Vietnam, and look for this path: Wings Over Vietnam\Objects\Aircraft\MiG-21MF, inside the folder look for MIG-21MF_DATA.ini, thi file will be open with notepad, then scroll down to Weapon stations and you'll find something like this:
// Weapon Stations ---------------------------------------------------------
[LeftOuterWingStation]
SystemType=WEAPON_STATION
StationID=1
StationGroupID=1
StationType=EXTERNAL
AttachmentPosition=-2.68,-2.17,-0.42
AttachmentAngles=0.0,0.0,0.0
LoadLimit=500.0
LengthLimit=3.5
AllowedWeaponClass=BOMB,RCKT,RP,IRM,FT
AttachmentType=WP<--------------------------------------here you need to add SOVIET, preceeded by a coma, so you'll have WP,SOVIET
ModelNodeName=WingPylon_Outer_L
PylonMass=60
PylonDragArea=0.02
LaunchRailNodeName=MissileRail_Outer_L
LaunchRailHeight=0.10
LaunchRailMass=25
FuelTankName=Tank490_MiG21
since there are more stations, be patient and add the same to all of them, then close it and try again, you'll see more weapons appearing.
if this is not working please let us know.
regards.