@IChen, at the moment, we don't have prop guards. There does seem to be products available on the market that would work with the S500 frame. You could 3D print some if the ones out in the market are not up to your spec.
I noticed you're looking for an indoor specific drone. Have you looked at the Seeker? That platform is more suitable specifically for indoors.
FYI, we are developing a smaller drone platform called the Starling, smaller than the Seeker and designed for indoor navigation and development.
Hope that helps