Dear Felix,

i think you should design the degenerate PCR primers. Try to serach the conserved motifs in rbcL, reverse translate it, design  the primers.

Degenerate primers is the way to go, but avoid degenerated sites near the 3' end (primer binding site). Also, design and order at least two forward and two reverse primers. The external primer pair can be used in the PCR and the internal primer pair for sequencing (or for nested PCR).

i think beside using two forward and reverse primer, you can also use a single middle primer for getting the full length sequence