How do I buy a billboard in India?

One of the answers mentioned mix of media owners and agencies (who collates media/billboards of 2–3 owners) and sell a pan India billboards plan to big companies at a margin.

If I talk about media owners, they are someone who pays upfront annual contract fees to authority and have sole rights on those hoardings and sell them. Usually these contracts are long term say 10–15 years.

Outdoor mediums are usually found in cities (highways, busy traffic junctions, markets, etc) on airports, Metro Train stations, bus shelters (Like BEST bus stands in Mumbai etc) cab branding, bus wraps etc

Prominent Media owners list,

At Airports,

1. Times OOH
2. TDI International India LTD
3. JCDecaux
4. Laqshya
5. Also, there are few more players who owns airports in only tier 2 & 3 cities.
6. City billboard owners are Bright Outdoor, Simca, In & Out, Proactive etc plus few of the airport media owners also owns city billboards too. Hope this will be little helpful.