if you are looking for unknown sequences you can try to use degenerated primers that you can design from published sequences (https://bitesizebio.com/18992/a-primer-for-designing-degenerate-primers/).
This might also be interesting for you http://aem.asm.org/content/58/11/3759.full.pdf+html
If you want to do it in vitro, then yes of course, you can use PCR. If you want to do it in vivo, you will have to transfect the plant cells (this is difficult because of the cell wall -- but there are protocols to do it) with plasmids containing the tRNA gene of interest. Alternatively, you can use transposon-dependent chromosomal integration of the tRNA gene of interest. HTH.