How to get business for the walk-in client in travel field ?

Put a sign out front and maybe advertise? Walk in clients need to know what you offer when they walk past your office if you want them to stop in, and you would have to advertise locally to let others that don't walk by your location know where you are and what you offer.

The old saw is location location location. If you want walk-in clientele you need to be place your business in a high pedestrian traffic area.