The best place to look is in the china and glass department of a good department store. In the UK both John Lewis & Debenhams have good selections. I collect decanters and often find good ones in charity shops too. If the decanter is going to be for spirits rather than wine make sure the stopper fits extremely tightly or your precious single malt will slowly evaporate!
i have two , i didnt realise they were hard to come by , then again i have had them for years and about to get rid off them , didnt think anyone would want them .