I'm assuming you are in Oz at the moment then. You can either google standard horizon and find a distributor close by or go to Whitworths and buy one through them. I think most chandlery stores will be able to order one for you if you don't go direct.
The AIS display is a bit on the small side but it gives you all the information you need including a nifty button entitled 'CALL'. If you press that, a phone will ring on the other ships bridge. It's a fantastic way to speak direct to the skipper of the other vessel. Usually if you just get on the VHF and call you will not be responded to but if you press that - they will answer. We did that in white out conditions in the midst of a huge storm off Papua New Guinea when we got an AIS alarm. The skipper answered and then thanked us for informing him we were on a collision course as he could not pick us up on radar. Between us both, we were able to work out who would do what to ensure safety of both vessels. Mind you they were a huge cargo ship and we would have barely scratched their paintwork!
As a side note, Singapore have now introduced a maritime law that all vessels (commercial and recreational) carry the ability to both send and receive AIS. Being up here in Borneo and planning on heading across that way next year, we may have to bite the bullet and get a dedicated AIS transponder