http://yacc.pspgen.com/Yacc_0_4_0_3.zip
i had the same problem, but converted the .cso to an .iso with the program above. Its free to download and simple to use I suppose.
btw i feel this a good time to remind you guys that sea of thieves was made by rare, who also made DKC1-3 and DK64, alongside banjo kazooie and conker's bad fur day