If you put System.Serializable and make the values public the struct is exposed, other then that. You would probably have to make an editor script to expose them.
[System.Serializable]
public struct Attachments
{
public Transform scopeModPos;
public Transform muzzleModPos;
[HideInInspector]
public WeaponAttachment scopeMod;
[HideInInspector]
public WeaponAttachment muzzleMod;
}
public Attachments attachmentConnectionLocations;