Hi,
Firstly I would recommend Taiwan as a place to teach English. It is a nice environment here, and still a good standard of living. It is possible to find work any time throughout the year, but obviously easier before the start of new semesters. The new year starts in September, but most schools have summer classes for a couple of months before that. A good time to look for work is between the end of June and September as a lot of schools like to try out teachers over the summer before signing them for a year. It is best to be in Taiwan before you start applying for positions so that you can go to interviews and check out the school before you decide on anything. There are several sites to find work. http://www.taiwandeal.com seem to have regular jobs posted, so just keep checking out the latest jobs available. Arriving in March might still be ok as you seem to have a lot of experience teaching.
Hope this helps. Good luck to you.