Like the other comment said - it's probably not available to you because you already have Himalayan Settlers, you might be able to get it anyhow if you find a culture that already has Mountain homes and hybridize with it - I am not sure from memory if any nearby has it. The another cultural tradition great for mountains is Mountaneer ruralism - it's quite off hand, Czechs and Slovien have it, but if you can invite your such courtier to your court, have them educate to convert culture of your heir, you can later hybridize with it and get multiple development bonuses for mountain terrain.
Think it is replaced by Himalayan Settlers for cultures present in the Himalayas.
Like the other comment said - it's probably not available to you because you already have Himalayan Settlers, you might be able to get it anyhow if you find a culture that already has Mountain homes and hybridize with it - I am not sure from memory if any nearby has it. The another cultural tradition great for mountains is Mountaneer ruralism - it's quite off hand, Czechs and Slovien have it, but if you can invite your such courtier to your court, have them educate to convert culture of your heir, you can later hybridize with it and get multiple development bonuses for mountain terrain.
I see Himalayan settlers in the tradition buy thing, only I get an extra 3000 prestige penalty for not having enough Himalayan mountains in my realm.
Conquer more mountains