As Nick says, the easiest way to check if an item is still sold is simply to type in the stock number on the Argos website:
http://www.argos.co.uk/
However, take care to check that the item description hasn't changed. I once made a special train journey to an Argos store because my nearest two stores were out of stock of the printer I wanted. I'd particularly selected this one as it was for a friend who needed a printer with a parallel port. I was half way home on the train when I noticed that the box stated the printer I'd bought was a different model and USB-only. When I took it back I pointed out that I'd correctly filled in the order form for the printer advertised in their catalogue. It turned out that they'd replaced it with a completely different printer (which was totally useless for my friend's needs) but continued to use the old stock number. As this was during the currency of a catalogue, they might do even more confusing things when catalogues change!
When will the next catalogue come out? Well, I've just checked the archive of their press releases. This year's Spring/Summer catalogue was launched on January 18, so I'd expect them to select a similar date next year.
Chris