Where can I find an "official" list of English graphemes?

If you look at the various spellings for each given phoneme listed in Wikipedia’s section on “Sound to Spelling Correspondences” in their article on English Orthography, this may help.

I’ve looked at both your PDF sources: the Wikipedia section is better than either of those. Your task is harder than you may realize.

I get what you mean because there are officially over 44 that include the American and British, but I don't know where to find it, and I'm looking for it as well. :/ But check page R45 of the Oxford Advanced Learner's Dictionary, you'll find it there with an example each. If you don't want to use a dictionary, then I'm sorry.