If you are very lucky, there are rich natural sulfur deposits readily available nearby.
An example of such a place is Indonesia and Eastern Java, where blocks of Sulfur can basically be picked up like rocks from the ground.
--> Note that such locations are very rare and will generally be colocated with zones of strong geologic activity/volcanoes/hot springs.
Outside of such very lucky circumstances sulfur is generally mined using various techniques.
There exist also various chemical extractions and processes used to gain sulfur:
... but let's be honest, none of these ways are particularly suited for someone in 'survivalist' circumstances. At best you will still need a lot of digging equipment, tools and knowledge for chemical extraction an detailed geological/geographical knowledge to know where to search for raw materials.
See for example this group, which travelled to Iceland to try and purify sulfur from natural raw materials.
With respect to how hard sulfur is to acquire in the largest parts of the world I'd go as far as to say it is of negligible significance in a survivalist setting.
- Short term sulfur/blackpowder needs are covered by what the survivalist brought with them or can salvage from surrounding areas
- On the long run the survivalist might be better of using tools that can be created from easily gathered natural resources (e.g. bow & arrow).