What is the tRNA gene copy variation between different yeast strains?

I'd take that computational angle and run the sequence data through tRNAscan-SE (Lowe & Eddy, Nucl Acids Res 25: 955-964). Ideally, you'd install this locally. This tool is what the UCSC folks use and it has been the best known, most widely used tRNA predictor for years. It's what we all used on Arabidopsis thaliana genome annotation back in the late 1990's.

There is also a genomic tRNA database that may have many of the predictions you seek, at least for some of your species/strains.