No substitute. You can get it online. I think I paid $20 for mine years ago (never goes off) and I've used probably about 1/20th of the bottle... and it's a small bottle.
I looked around for ages trying to find it. I doubt you'll find it anywhere here but online.
I get mine from one of those shops that sells lots of lollies and stuff imported from the US. I guess they also import liquid smoke from there along with the piles and piles of chocolate and lollies and pop tarts
Hi Deborah, I'm not sure what part of Queensland you're from but The Green Edge at Enoggera usually sells liquid smoke (that's where I got mine) and the Vegetarian/Vegan Society of Queensland also apparently sell it (http://www.vegsoc.org.au/product_list.asp?ProductID=70).