: It seems that top quality Sitka Spruce is what is used to make the tops and
: bottoms of guitars.

Yes indeed! Old-growth wood with no knots preferred.

: In order to insure a steady supply of this wood the
: instument makers buy the best trees long before they are ready for
: harvest.

I don't know about that...the problem is, instrument makers don't use very huge quantities of lumber, board-foot-wise. They do pay top dollar for perfectly quarter-sawn old-growth spruce soundboards, though, that's certain--and the lumber suppliers have figured that out. Some makers are using western red cedar and redwood tops, although for tonal as well as economic reasons. On some of the guitar builder forums I frequent people mention scrounging scraps of spruce for bracing from suppliers of aircraft wood. Here's a link to such a supplier, if the html code works: http://www.aircraftspruce.com/catmain.php?dest=cathome.html .