Hello Lucie,
It all depends on what you want.
If you're specifically looking for copperplate exemplars, I suggest you go to this post on my blog.
https://pennavolans.com/the-10-copybooks-you-need-to-know-about-if-you-study-copperplate-english-round-hand/It's a list of my favorite copybooks on the subject. It should help you pinpoint the kind of copperplate you would like to work on (you'll see that the style changes from the Universal Penman in 1741 to 19th century French / Spanish / American interpretations of the hand).
I would just also add this book to the list, I don't know why it's not in there...: BECKER (George J.), Becker’s ornamental penmanship, 1854. (
https://archive.org/details/ahn2554.0001.001.umich.edu/page/n5)
Once you know which style you like, I suggest you stay on the same site and visit the Bibliography (choose the time and place that fits your needs), where you'll find links to many more copybooks.
If you're looking for a mix of different hands, models to choose from..., then I suggest:
TSCHICHOLD (Jan), Treasury of calligraphy, 219 great examples 1522-1840
JESSEN (Peter), Masterpieces of calligraphy, 261 examples, 1500-1800
Both books were published by DOVER and are not published anymore, you should be able to find them on the secondary market.
If you're comfortable with French, I recommend Claude MEDIAVILLA, Calligraphie. It's a big book with nice examplars (although they're not very practical to use) and beautiful photos, there's also lots of info on the history and the penmen.
There's no mention of Spencerian in either of these books: you'll have to look for the book Erica mentioned, or Michael Sull's Spencerian script volume II (volume I is also interesting, but with less models).
Good luck!
and thanks
@Estefa for mentioning Penna volans

!