Here is the complete text of the rules (from http://5e.d20srd.org/srd/equipment/equipment.htm):
Arcane Focus. An arcane focus is a special object – a globe, a crystal, a wand, a purpose-built stick, a wood-length wand, or something similar – designed to channel the power of arcane spells. A wizard, a warlock, or a wizard can use such an object as a spellcasting focus.
Focus Druidique. A druidic focus may be a sprig of mistletoe or holly, a rod or scepter made of yew or special wood, a stick drawn from a living tree or a totem object incorporating feathers, fur, bones and sacred animal teeth. A druid can use such an object as a casting target.
A super-literal reading of the rules would say: an arcane focus is "a wand designed to channel the power of arcane spells". A druidic hearth is "a wand made of yew or some other special wood".
It looks like you could go find someone who can create arcane homes and ask them to do an arcane focus from a length of yew wood. Then, because of his yew wood, he will also work for druidic spells.