VBIOSs are released by the manufacturer and are tailored to that specific make and model. Often there are no official new BIOS files released publicly, as there is very little contained in it, unless there is a widespread issue, such as fans not working or improper settings loaded, or, in the case of the 5600 XT, an AMD sanctioned performance update issued after product was shipped to stores. You should not touch it unless you are having a problem, as you can brick your card very easily.