Most larger cities round the world have high street language institutes or cram schools. They are very often located nowadays in shopping malls too. They don't have to follow the mainstream school holidays, and they offer courses 7/7. As most English language courses are divided into modules of 30 hours or so, you might be lucky and get on to one of those, which lasts for 4 - 6 weeks depending how the school owner has spread the lesson load throughout the week.
You could also find out about extra language courses that mainstream schools offer for their pupils during the various school holidays. As Alex says, Google is one of the first stops on your travels.