Hello ExE Boss, not sure whether this is right place to go, but I'm posting here as you've edited the Manual:ISBN page.
I suggest including in the Individual booksellers section of the Book source Special Page an ISBN search in the company Wordery whose website is wordery.com
Like Amazon, Wordery has a large selection of English-language and non-English language books available. Unlike Amazon, they only sell books and do not have individual country pages aimed at customers in different countries.
I do not have the technical knowledge to add a Wordery ISBN search, and would not wish to do so if for some reason this contravened Wikipedia polices. I have no connection with Wordery other than being a customer.
So if this sees to be a good idea to Wikipedia, would you add Wordery to the ISBN search pages?
Hope this helps.