What Shellybean said... and you get more in Felucca, too.
But, here is what I've had the best luck with...
Find a convenient low-travel area with lots of trees and chop every tree until it gives no more wood. This causes the wood to respawn with a chance to have a rare color. When you find a tree with the color you want, don't take every log from it to keep it from respawning into another color or just plain wood.
And use the EC with easy to drop map markers or use the UOCartographer to mark trees with color wood and number of logs.
This will take a while, but I now have a large area with every color wood in it, even several frostwood. The hardest part is not to be greedy and leave that last log on the tree.