Hello Sunny and welcome to the forums.
Brother, I'm from Lahore too. But I'm afraid I'm not entirely sure where to find a good & honest mechanic whose specility are Ravi 125's. But have you visited the motorcycle market around Lahore Hotel (near Hall Road and Railway Station)? It would be my best bet... If you can't get something done there thats related to motorcycles then I'm afraid you're out of luck!
Anyhow, good luck with your bike. And brother, I mean no offense or any disrespect, but bikes like these need LUCK more than anything!
Few years back, a very close friend of mine read some forums on Pakwheels and elsewhere, got excited and threw away 100k on a blue Ravi Piaggio. Its was a great ride initially, no doubt. He'd often come to me on his Ravi, giggling to the ears and would start bragging about his sparkling Ravi! Now, Fast forward to an year, and he sold it for mere 65K!
Why he sold it? Well, I shall not disclose it here but since its a Chinese Bike; everyone here can guess WHY EXACTLY he sold it!!!