Meshes would be in the textures folder, and for the entity file under the gameinfo folder find the entity file for your particular starbase the mesh instructions are there down near he bottom of the file look forIts all under the Meshnameinfocount line

MeshNameInfoCount ##
MeshNameInfo
    meshName ""
    criteriaType ""
MeshNameInfo

Are you using Entrenchment or Diplomacy vanilla sins doesn't have Starbases

I know it seem like a dumb question but I had know idea so I had to ask. Entrenchment and Diplomacy are basically mods to the original sins. Entrenchment had the starbase add on and while diplomacy has starbases I believe it just uses the resources from entrenchment so to find them look in the entrenchment folder\gameinfo