Hi llewellin, I can maybe help you a little bit with European coins.
According to Levinson's "The Early Dated Coins of Europe 1234-1500", there were two groschens minted in Saxony with the date 1457. The specific references are I-91 and I-92 and they are a bit spendy--somewhere in the $3K to $5K range for the typical aVF condition. It is an understatement to say that they are rare, the more common one (I-92) is thought to have something less than ten coins available outside of museum collections. If you ever saw one for sale, you would want to get lots of assurances of its authenticity.
If those don't excite you, there were three dutch coins minted with that date as well (III-22, III-23, and III-24). These are just as rare as the German coins, but at about half the price (probably due to lower demand).
Finally, the Austrian Duchy of Wiener Neustadt minted a kreuzer with a 1457 date. It is uncollectably rare.
You seem super-fixated on this one specific date, so an alternative pathway would be to focus on the French royal coins as in some cases, the specific emission can be bracketed to a specific year (despite the date not being on the coin). You'd need to study a reference like Duplessy's "Les Monnaies Francaises Royales" two-volume set. I believe that Charles VII was in power for 1457.
Best of luck!
"If you climb a good tree, you get a push."
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz