"Would" comes from "will", both forms being very ancient indeed. "Can" is Germanic only, but ancient enough; its past tense should be spelled "cound" (as in German "konnte" or Dutch "we konden"). Maybe this spelling was considered too close to some four-letter word, or, more likely, was absorbed by the magnetism of "would" and "should".

But I cound google

8 tricks I cound never do before I got my Fullthrottle Dual Caliper Handbrake

Coundn't be cuter.