So far the key resource for me has been "Macintosh C Programming by Example,"[0] which also uses THINK C. The disk that originally accompanied the book is available on Macintosh Garden.[1]
Scott Knight also has a nice intro to classic Mac development, using Pascal in the Macintosh Programmer's Workshop instead of THINK C.[2]
Then there's also the old Inside Macintosh books[3] and other how-to books[4][5], but I haven't looked at those yet.
[0]: https://vintageapple.org/macprogramming/pdf/Macintosh_C_Prog...
[1]: https://macintoshgarden.org/apps/macintosh-c-programming-exa...
[2]: https://knight.sc/software/2020/04/19/classic-macos-developm...
[3]: https://vintageapple.org/inside_o/
[4]: https://vintageapple.org/macprogramming/index_year.html
[5]: https://macintoshgarden.org/apps/learn-c-the-macintosh-0