What are you working on?
There's two different "early A body" wagon styles- the '60-'62 "Road Toad" Valiants and Lancers, and the '63-'66 Valiants and Darts. Sadly, the answer is the same for each; but it will help in your search to differentiate between the two.
I have not seen them anywhere for quite a while, even from the Australian vendors- most of them that I had on file have gone away, with dead links or abandoned web addresses. Maybe one of our Australian members can shed some light on any availability that they know of.
Your only recourse at this point (that I'm aware of!) is to browse the listings of Metro, Steele, SoftSeal, Precision and the like to come up with a profile from their "bulk seal" listings that closely approximates the original; and make your own. There's still glass shops out there that will do this kind of work for you, too- but they're far and few between. You're on your own in that regard. Best bet is old independent installers that still have a few of us old guys on staff, and are willing to spend a little time fabbing up some seals and installing the glass for you. This used to be somewhat common, but not so much anymore.
And if it was me, I'd have them install the glass too, since any mistakes or damage to the glass will result in another seemingly futile search for the "unobtanium" quarter glass...
Best of luck to you!