There is a crowdfunding campaign going on to fund a set of Call of Cthulhu 7th edition adventures cum background set in colonial Vietnam, circa 1925-1955. Some content is specific to WWII-era adventures, but some ideas could easily be stolen for a TCE/CoC cross-over game set in Vietnam, in particular the Hòa Hảo Buddhist militias, the entities that offer the temptation of enlightenment, the Expédition Lemont to the mythical city of gold, and the possibility to tie in the Plateau of Leng with Southeast Asia.
See p128 of The Celestial Empire for further details on running cross-over adventures with the Call of Cthulhu game.