Rob, Sigmfg.com is a good place.
I also like
http://www.lonestar-models.com/ and recommend them as well.
Lone Star is also a great sponser of this site.
Control line planes really benefit from light building and light construction materials. This said, when you can spare the weight in some areas or applications, Tower Hobbies served me well with some inexpensive bundles.
The biggest problem with finding 'good wood' is being able to select it yourself and buying from the sources I have just mentioned it simply is not possible when ordering by post.
Good wood is also dependant on what the seller has in stock and has himself been supplied with. Balsa varies so very widely in both density and grain that it is a crapshoot for the suppliers. This means that at any given time, one supplier will have better stock that the rest and that can change in a days time as supplies are sold.
Specifying contest grade is of course the best way to go to get the lighter pieces but then some of the light stuff will be spongy and structually useless. These can be best used as blocks for cowls and wingtips.
Robert