They use a custom script (with Javascript frameworks), so you won't find it on the web free (or paid) to download.
However, it's not a difficult website to create for anyone knowing his job. I mean, any developer can create the same website with a CMS such as WordPress and a good-looking template. I advise you to rather follow this path.
I didn't see the member area so don't know how it looks like but I don't believe there is something so difficult to reproduce.
Good luck