It's a question asked previously as there is definitely an interest. For whatever reason those 'middle years' (my favourite) 1970-4ish are excluded from itunes. They are available on cd etc., as MTM and BT discs are around $7 from Amazon US.
From the previous related threads I don't recall a reason for this. As others have said, there is money to be made, Mick!!
http://ledge.fleetwoodmac.net/showth...e+trees+itunes