Buying Round the world tickets

Presume http://www.roundtheworldflights.com/ is who you mean.

Any large travel agency or OTA will be able to deliver the same thing, or look into the what the big airline alliances offer in terms of air passes for specific continents or comprehensive RTW ticketing options. Don't discount the use of low cost carriers too, especially in Asia & Europe.

http://www.staralliance.com/en/round-the-world

https://www.oneworld.com/flights/round-the-world-fares

http://www.skyteam.com/en/round-the-world-planner/