Project TBR looks up availabilities at all your libraries for all the books on your TBR -- and shows you the best availability for each one.
Goodreads instructions: paste a link to your Goodreads profile or any of your bookshelves. Or enter your Goodreads profile ID (the numerical ID identifying your account).
Storygraph instructions: enter your Storygraph username, or paste a link to your Storygraph profile or any of your book piles.
From the iOS app, you can get this link by going to My Books > Want to Read > ... in upper right corner > Share > Copy