FJ Gray division of O'Bryan Glass offers anti-newton ring glass.
http://www.fjgray.thomasregister.com/olc/fjgray/
Their description of their glass is...
Anti-Newton Ring - This is a thin float glass substrate with a very fine acid etch to one surface to eliminate the Newton rings caused when two pieces of float glass are put in contact with each other. These sheets are approximately 24" x 24" and are available in 1.5, 2, 3 and 5mm thick.
Vertec, a Belgian firm, is a large European maker of thin glass, and a specialist in anti-newton ring glass. They have sales reps throughout the world.
http://www.glaverbel.com/en/product/thinglass/thin.cfm
Glaverbel is the conglomerate name... Vertec is the specialty glass division.
Focal Point, in Sanford FL, claims to be the nation's largest distributor of anti-newton glass. Their prices are remarkably unattractive. They want $42 for a 5x7 sheet and $89 for an 8x10. So that's well over $1 per square inch.
Their web store front is Light House.
http://www.fpointinc.com/cgi-local/web_store/web_store.cgi
Anchor Optical...
This is an excellent source for surplus optics, including flats and (occasionally) AN glass.
http://www.anchoroptical.com/
http://www.anchoroptical.com/Products/Display.cfm?catid=247
This page shows 3mm optical flats of large format size for $9 plus $5.75 shipping. That sure beats the prices from the enlarger vendors.
So here's the problem.... I need a new negative carrier for a large format enlarger. In fact, I need a couple of them.
The classic book style glass carrier has Anti-Newton glass on the top and an optical flat on the bottom. But the prices out there are lunacy.
This kblog discusses the sources, the design issues, the advantages and disadvantages. It also gives web links to spots with good information.
