A note on Japanese content: the Japanese SC4 community is a tight-knit community well-aware of the members who have and had contributed to custom content with SimCity 4. However, a lot of them are pretty sensitive to their work and proposed that any of their work to not be hosted on Simtropolis or any other website other than their own unless we are granted their permission. That extends to any of the dead sites like NOBs and Kei's (hide-inoki actually went out of his way and contacted him by email and phone so that he can be granted permission). I can extend my arm to the community and ask existing members if they will be willing to share content but so far I had received a negative response.
SimCity China has their website still up and there's still a lot of activity in the forums so keep that in mind. They're the largest or the second largest SimCity community, honestly.
Linking is fine but uploads are a different problem altogether.