Apparently if you buy direct from Terasic you can get hold of them. The downside is a large shipping cost and import duties/taxes on top. I have heard of people successfully getting them shipped from Terasic offices within the same country as them to avoid the import duties issue.
The Terasic boards are essentially an evaluation board and despite the recent price increases, still give you a lot of hardware for the money. Other boards that come close in capability and have what you'd want for something like an emulator platform (like HDMI out) are a lot more expensive. Pretty sure Sorgelig (project lead) has said he has no interest in ever porting it to a new platform. Doesn't mean someone else couldn't, but it would be a major effort to do so and keep up.
There’s a required RAM module for most cores that slides into the de10 nano. The software and the Linux kernel are also tightly coupled. Individual cores can be ported to different FPGAs though. The SNES one for example was recently ported to the analogue pocket.
