http://www.kaymont.com/pages/cold-weather-balloons.cfm - have sent an enquiry to them. Their balloons turn up on ebay for about $30.
http://www.yunhuanelectronics.com/Meteo ... ctured.htm
http://www.alibaba.com/showroom/meteoro ... lloon.html
http://www.hwoyee.com/
http://www.hydrometeoindustry.org/catal ... roduct.htm
http://www.scientificsales.com/Meteorol ... n-s/25.htm