The WD33c93 is basically a single-chip SCSI Interface. Replacements are aroud, even pin compatible alternatives. Some even improve speed and compatibility.
The 390563IC is a C= made one, if you need one of those best bet would be to buy a defective or cheap A590 or 2091.
Yes, the 2091 is basically the same controller in different shape, you can use it to repair a 590.