22,000 books divided by 500 per day equals 44 days. If you haven't found a tool by 2 October, it would have been better to just do 500 per day. Maybe a note to the folks at
info@ejelta.com who wrote and maintain ISBNdb to ask for a one-time 22k authorization.
Doesn't Calibre also try to use Google Search to find and attach book metadata. I know it uses ISBNdb. If you DO FIND another good ISBN search tool that grabs blurbs and summaries, please alert us here and the fine gent that develops Calibre so us mere mortals with a few hundred books can enjoy the benefits you find.
I'm willing to do some of the searches for you on my ISBNdb license of 500 per day, but I don't know a method without being very labor intensive. Tell me if I can help and that would cut you back to 11 September.