You could try electra (smiths commercial) or builders hardware, i will try them on tuesday for you.
You could use a double thickness of say 12mm ish, cut the base into three bits and then put the top on in two bits, so you have a nice big over lap.
You should be able to get these sheets at about 45 +gst.
By the way, that glass price was the best one.
And glasstec can't get 12mm low Fe.