OMSCS Open Courseware

I once considered applying, but I gave up because collecting letters of recommendation was a major hurdle. My academic advisor from university has already retired…

How do you all deal with this?

I don't think OMSCS is that selective. Get a couple of letters from your former professors and/or bosses. Letters are supplementary, not the sole determinant. More than the letters, they likely care about your GPA and GRE.