My local library system has most of the original AD&D books. Look:
That's the assortment - DMG, PHB, D&D (top L-R), MM, FF, and MM2 (bottom R-L). They have two each of most of these.
That Dieties and Demigods book is the good one - Melnibonean Mythos and Cthulhu Mythos, too. I better warn them to make sure it doesn't walk off.
So support your local library - don't have the AD&D books? Use theirs. Taking them out will ensure their circulation numbers are up, so they'll keep them on the shelves, too. You can check out the books they have - I know the old library system I was in has the LBBs on its shelves. What about yours? Don't overlook your local library as a place to find gaming books.