they are available in Karachi at the 2 shops selling mitsubishi parts - they also cross reference to a diesel engine mitsubishi makes. There is a whole market of just mains and big ends in Karachi plaza market which will usually have them too.
edit,, I think they are shared with the 4D68 (galant diesel engine) - I know it works for the wrong mounted 4G63, cannot remember for the correct mounted one.