Hello again Mark,
Thanks for your interest; I wish I could mark you with a helpful star for you deserve it, but I'm not the original poster.
My set up is very simple and not that large. I have only 6 (yes, only 6) individual iTunes purchases, all the rest being ripped from LPs and CDs etc from my collection. So I'm not sure a separate folder could be justified.
In the old iTunes set up, the album artwork (even from some obscure albums} automatically appeared once the music was in my library so it wasn't necessary to go hunting. And this of course, is the nub of my problem (and probably the reason why iTunes couldn't care less).
Incidentally, Google and Amazon can be useful resources for album artwork.
I'll look at this thread over the next few days and if I come up with something I'll post back.
Thank you again. Happy New Year.