Are there any voices available for Captivate beside NEO Speech?
No. At present the built-in voices for Adobe Captivate are from Neospeech (now called Readspeaker). They sell other voices. You need voices that are compatible with the Voice Text product. https://www.readspeaker.com/solutions/speech-production/voicetext-editor/
If you're willing to do the text-to-speech outside of Captivate, I've really liked the choices available now in Vyond. Sadly their latest update made it MUCH harder to navigate to the voice you want, but once you have that, I've been typing it in, extracting the audio, and then using it in Captivate. It's a big of a headache, but the voices are more enjoyable (and language diverse) and it's cheaper than hiring an actor.