You mean this board?
https://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=183&No=30#contents
It is not an Intel/Altera product, it is a third party product made by TerASIC in Taiwan.
You can buy directly from them, or thru US distributors like Mouser or DigiKey.
As indicated, that board is obsolete and not being produced anymore.
The web link above has links to full board user manual and schematics, that might help.
Warranty? Doubtful unless you have the original purchase documents.
That board is old techology (CycloneII) anyway. You have to use an old version of Quartus to use it.
Better choices would be a DE0-NANO or DE0-CV for learning now.
https://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=163