Single copy housekeeping genes
Just flying from the waist: filter approach:
If there is a data source that has the expression data for cells in multiple tissues for any organism i would use that to find the housekeeping genes by sorting which genes are expressed in the greatest number of cells (think excel or XML). Next, I would check which of those genes are also found in/similar to the respective gene (homolog I thin its called) in the plants (using genome browser, e.g., ensembl and blast or just look it and click on the button to bring you to the plant genome). If your model organism does not have sequenced genome... get primers and see if you can sequence it for yourself to see if its there. Then check to see if its a single copy. Hardest part is finding an expressome database spanning multiple tissues in an organism to find housekeeping genes - then hoping they are conserved to the plant. Alternatively, you can consult literature to find housekeeping genes.

You probly just wanted a listing of the genes... sorry.