The Ledge - Few PRE-75 Albums Available for Download

I have been a Fleetwood Mac fan since I was a small child in the 70's. Throughout the years, I have bought and owned Fleetwood Mac music in the form of LP, 8 Track, Cassette, and CD's. Sadly, in keeping with technology, these formats have all but disappeared from my music collection. The Fleetwood Mac CD's that I own gather dust in a corner.

I now purchase all music through downloading and stream through BLUE TOOTH AUDIO in my car and at home. Although I resisted this, IT IS SO EASY AND CONVENIENT. No more lugging cd's around!

PROBLEM: Why can I NOT FIND any PRE-1975/Bob Welch Fleetwood Mac music available for DOWNLOAD on iTunes or Amazon. I would LOVE to add classic albums like "Bare Trees", "Mystery To Me", "Heroes Are Hard To Find" and "Future Games" to my IPhone5s playlist. While I have been able to find classic Mac albums like "Mr. Wonderful" and "The Pious Bird of Good Omen" on ITunes, the rest of PRE-Buck/Nicks music remains largely unavailable. WHERE'S THE LOVE? Can someone tell me where to download these tunes?