The Phylogenetic Handbook ( https://www.cambridge.org/core/books/phylogenetic-handbook/A9D63A454E76A5EBCCF1119B3C56D766 ) includes sample data sets. But searching for those data sets now, it seems that they are not currently available online at the URL given in the book (www.thephylogenetichandbook.org ).
I have attached an alignment of vertebrate mitochondrial genomes. Be aware that mitochondrial DNA evolves roughly 10-fold faster than nuclear genes, so silent site saturation is evident when comparing fish, amphibians, snakes, turtles, mammals etc. The mitochondrial genomes are great within the past 150 million years or so, for example just within the mammals.
The TreeBase is a great place to find good data sets along with published analyses of them ( https://treebase.org/treebase-web/ )