Greetings, all -- my first post on discovering OF. French editions are (or used to be) the most generously sized, from Dallier's Cinq Invocations to the Dupré edition of Bach. Maybe the answer to the question should be obvious: In my 20-30 minutes surfing this forum, I've collected four great-looking sheet music sites, most or all offering FREE masterworks in PDF or whatever. Besides this, it's much easier to hunt used or pre-owned hard copies in the digital age -- eBay and even Amazon seem to have plenty (even the Dickinson organ method). Organ sheet music CDs are out there -- you get a giant collection of PDFs for $10!
When I was in music school, one or two classmates freely ripped off top-dollar French organ scores from the University store. In just a couple of years the prices there went up by about 50%. Coincidence?
For those who, like me, have to have full-size "original" print editions (and the newer the better) -- AND are willing to take a shot in the dark -- there's the sale music and book lists at organlibrary.org. I've gotten some sensational things there and lots of crumbling papyri. But overall this cheapskate is very pleased with it.
BTW, don't call yourself an "idiot" (whoever that was) for loving grand old scores with beautiful graphics, calligraphy, associations, and a whiff of antique mold. Idiots love newness for its own sake. Idiots throw out any choral music written before 1990 and feed their singers on publishers' potboilers by subscription, most of which modulate a step up 3/4 of the way through and are printed in blue, green or maybe maroon for Lent.