I have been using a twin cap t-free dual sided tea mug for over a year. It does a passable job.
http://www.ebay.com/itm/Travel-mug-T...item337d0242de
While I prefer the taste of loose leaf tea made in a ceramic container or glass, this leak proof and shatter resistant one is just easier for me to commute with.
It can also be found on amazon.co.jp and rakuten
http://global.rakuten.com/en/store/s...item/10001307/

Another option is this folding silicone tea steeper insert
http://www.amazon.com/The-TeaSpot-St.../dp/B00367WDCC
It can fit in some paper cups so you could order tea with teabag on the side and use your own loose leaf. Good for those who travel light.