Sacky
I had the same situation as you. I can read up to 9 Ishihara plates depending on the lighting sometimes more. I sat the last chance lantern test at the Melbourne School of Optometry (I had to request this test through CASA) and passed. This test was similar to the farnsworth however it only gives red and white lights. It was over ten years ago now and I have heard the practical test at the field is also an option now and is probably more common. Whatever you do don't rush in, find out as much info as you can before any test, if you are going to do the practical test ask the guys at the tower to give a run-through a few times in advance. This may be organised through your flying school. The extra effort may be the difference in career as pilot or career as something else. Remember you only have to pass it once and you only get one chance to pass. Contact me by PM if you want any further info.
Good Luck