i would suggest to get a new shield instead of buffing as it will last only few months.its mehran so it wont be costing fortune ...
if you still insist...you can go to tariq road liberty market(ac market) and ask for it..there are one or two ppl there who do it
else main plaza but you need to check there 1st as there are many thugs out there....
you could find few on aisha manzil car market also.....but you need to ask around