Eglinton Engineering at Magill work with Ti - they may be able to help you out. Ask for David or Ian.
Hi again Blake, I've consulted a friend here in Adelaide who is a noted frame builder and repairer and a master welder. He strongly suggests that a repair to any Ti post not be attempted by welding. I suppose that it would depend a bit on where the crack has developed and how badly your friend wants to retain the original post, but he says that welding is generally not advisable simply because the stresses involved are so high. If the crack is in the main tube of the post he suggests a better fix would be to glue an appropriately sized aluminium post inside the Ti one with some sort of strong epoxy. I can put you in touch with my mate if you like... Much more secure! Sam.
Thanks very much for your reply and for the advice. It would be great to have your friend's details.
Might as well throw it in the rubbish if that's the case, presumably a titanium seatpost is desired for qualities of low weight and good compliance, sticking an aluminium tube up there isn't going to do that any favours...