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Paul, have you tried
http://www.realdiesels.co.uk/listerparts2.html ?
I assume you are looking for the bush with part number 5-1/D7A or no. 8-4-7-1 .
It fits all CS engines including the 8/1 and 16/2 with 4.5" bore, but not the 3/1 engines.
They quote a price of 28 Pounds Sterling not including shipping to Canuk land.
So it might be a bit spendy, but it is the real McCoy.
Not sure if they still have it, but it seems that when they run out of something they take the price off the web site, so they may still have it.
Peter might have better luck.
No connection to the above outfit just like the real stuff, it is of a known quality, not sure of the Indian metalurgy .