Hi Ramit! Advertising is broad, and I'm not sure which type you are looking for: online, print, tv or radio. Can you clarify?

Otherwise, your best bet would be to contact an advertising agency. They would be able to cater for all types of ads. Even a small agency will be able to do loads for you, and help you with specs for specific advertising you're looking for. 

You can try putting in a quote on this site, and you'll get agencies to get in touch.

Good luck!