Where can I publish corrigenda for a conference paper?
If the proceedings is one that was issued by the conference at the same time as the conference (or shortly thereafter), you may be stuck with just publishing it on your website, which is presumably what you meant by a tech report. If the conference was run by a major society, you may at least be able to get the online version of the proceedings updated. You should get in touch with the program chair for the conference at the very least.