As a Firmstrong bike owner, Firmstong is good quality bike at reasonable prcie and I don't know about greenline but all kent/shcwinn/huffy cruiser are department junk bikes ,avoid all those brand if you are looking for good quality bikes.
You can find firmstrong on amazon.com , ebay.com , beachbikes.net or mybeachcruiser.com
Shop around for best price. Good lock!