The file download seems to work fine from the page you linked at the present time, from within California, with a Windows 7 system running Firefox.
Purely by observation, based on occasional forums posts, there seem to be problems at times with content delivery outside the United States. Are you attempting to download from outside the United States? If so, which country?
[Later:]
Sorry, I spoke to soon. After trying some additonal links on that page, I get “service unavailable as well” for some of them. I know of no way to alert NVIDIA to this issue. If you are lucky, an NVIDIA moderator will find this topic and follow up internally.
I am sorry for the late reply. I fixed it by downloading CUDA toolkit version 10.
You don’t need to worry about the version of CUDA toolkit because almost versions are supported by gpgpu-sim. According to the official gpgpu-sim menual in gihub, it is specified what versions are supported now.