ShelterBox's HQ is in Cornwall in the UK.
There are 11 international affiliates.
You can link to their websites below:

ShelterBox is an international disaster relief charity that delivers emergency shelter, warmth and dignity to people affected by disaster worldwide
TRACK YOUR BOXOur goal is to help 500,000 people every year. So far we have sent out this many ShelterBoxes
ShelterBox returning to Guatemala after mudslides
Fresh disaster leaves Central American country reeling
ShelterBox volunteer speaks after New Zealand earthquake
The ground was still shaking when ShelterBox called, says SRT.
Initial aid for hundreds of families arrives in world’s poorest country
ShelterBox Response Team and 200 boxes arrive in Niger.