OI :D
Ive made that search too and I have seen most of them, but it is so unorganized... Was hoping that we could make one post and maybe it could be made sticky,
There have been several threads showing all the free-trade fiefs. They last for a couple months then the thread starter gets bored (or a better thread gets started) and they stop being updated.
http://forum.melee.org/diplomacy/sumbuja-and-rebache-free-to-trade/
http://forum.melee.org/diplomacy/apostates-trade-permissions/
http://forum.melee.org/diplomacy/shu-han-open-trade-fiefs/
http://forum.melee.org/diplomacy/wars-and-alliances-na/
http://forum.melee.org/diplomacy/(eu)-compilation-of-maps-and-wars/
http://forum.melee.org/diplomacy/werfrieds-peasant-battalions-diplomacy-thread/
If you want to rely on free-trade fiefs it's your responsibility to check the diplomacy section and keep up to date on which fiefs are free-trade and which aren't.
Good luck!