Do you mean that it was such a long time ago that the purchase is not on your list of purchases any more? You could change the view from default (last 60 days) to 2021 or even 2020.
You could also look at your emails, as they usually send an "Your order is confirmed" email (with the seller's ID) after you purchase something.
As for "websites", not all eBay sellers have one, and if they have one, they are not allowed to share the link if people can also purchase from their website. But I guess you probably just need their eBay page?
If you had a problem, you have 30 days since the last day of the estimated delivery to open a case with eBay and 180 days since the date of purchase with PayPal (if you used PayPal to pay of course).
