What I do is take any sentence that has an audio-clip, and you can right-click the play button and selecting “Save Link As…” or something to that effect. Then you’ll have the file. In Anki, when you add the card you can copy/paste the sentence and meaning in as you need and in the Audio part you’ll want to click the paper-clip icon in the toolbar. That will allow you to select the file you just downloaded. I’ve heard about using software to make audio files for sentences that don’t have audio, but I’ve not really wanted to try that approach out of fear that it would teach me the wrong way to say something.