Vendors for items such as latches, hinges, corners, and handles suitable for Eurorack and 5U modular cases.
(in no particular order)
ReliableHardware.com sells a wide variety of parts for cases, including rubber feet, hinges, latches, Tolex and glue, etc. They also have some videos on their website showing how to build cases using their parts.
Reliable Hardware also lists some items at Amazon.com (affiliate link) – Sometimes you can get items faster or cheaper here.