I walked into my local BORG, located a materials cart, and went to the sheet goods section to buy some 1/4" birch plywood and 1/4" MDF. I looked around for awhile and a young man came up and helpfully asked whether he could help me. Sure, I said and told him what I wanted. He replied that they don't stock those any more. As I stood there speechless, he offered my hardboard instead of MDF and showed some yellowish looking plywood (all very warped). He did not know what kind of wood the yellow plywood was, but he knew it was from China. He then told me they had some of what I wanted left over cut into 2x4 foot sections, which served my needs for the moment, but....
As I wandered about I also noticed that they are now stocking plywood in metric thicknesses. I really don't know how to substitute for 1/4" birch, which I use a lot of for cabinet door panels. Oh well, the good part of the story is I now have almost no reason at all to enter a BORG. That's worth something!