You go to the police chowki which was mentioned in the lost challan form with an affidavit stating the fact that you lost your challan form and despite your best efforts you couldn't find it, and in case you do find it you wont misuse it yaada yada yada. In my case they have taken the affidavit and my cell no with it and have asked me to come back on Sunday if they cant track my license before that and give me a call. I was hoping that I'd get new challan forms right then and there as I was led to believe by my source but that didn't happen. I'm not at all expecting their call so will go back on Sunday to see what more needs to be done.
I have a feeling that yeh guthi F-8 kachehri ja kar hi khulai gi eventually. Lets see.