I ended up buying a 30 litre Roban(sp?) urn as all I found on eBay and trading post etc were small 5-8 litre ones.
I bought it at a kitchen supply store on King Street Newtown in Sydney though.
I know that Linz managed to score a 20 or 30 litre one from somewhere.
Your best bet would be to go to monitor the auctions at Grays Online. You can setup notification for auctions based on keywords.
They auction off items from businesses gone bust like caterers and restaurants etc.
I've seen them in their auctions before but never been able to make one.