It's likely a very very small group, but I am certain there are some ultra high net worth members of HN that are SpaceX investors, either directly through family offices, or indirectly through private equity funds.
It's also pretty easy to invest in them indirectly. There are a few Fidelity funds that include SpaceX, and you can also invest in other companies that invested in SpaceX (ulterior motives, including my employer)