You may visit Chah-E-Sultan, Kamran Market, etc. in Rawalpindi for that. It may cost somewhere between 8-15,000 PKR (huge margin), but first visit and survey the market, and then buy after bargaining / negotiation from the shop which offers least price.
I would never suggest and recommend it. It has been installed for some reason and removing it will jeopardize its intended function. The voice of exhaust will also change and mileage can get affected.
5w-30, API SN, Fully Synthetic engine oil from any reputed brand. For best for bucks, Total Quartz 9000 Future Series, and change with genuine oil filter after every 5,000 Kms.