It's my understanding that Seachem does not sell directly to the consumer. If you go to their website and look up Kanaplex, they provide you with a product description and then a link to look up possible dealers in your area: http://www.seachem.com/Products/prod.../KanaPlex.html
The problem I experienced with this is that even though they provide a list of dealers, sometimes that list is outdated as each dealer page mentions that the dealer carried the product when they were last visited by a Seachem representative
. In my case that was about 3 years ago for many of the dealers. But it may be worth your time to call some of the dealers in your area to verify.
If that fails, I think the only other option is ebay. Here's the top link that returned when I did a search for Kanaplex on ebay: http://www.ebay.com/itm/Seachem-Kana...item2a2add1a4e
I have no connection or experience with this seller, but they do have a high rating.
But I am not an expert on this and I'm not sure if Kanaplex is the answer. I mention this based on my experience and in support of what Sakura8 said about it being very difficult to find.
From the photo it looks like your fish may be exhibiting signs of dropsy. But it's probably best to let the others have a look before you go by my diagnosis.
Edit: Here is another site that sells Kanaplex: http://www.drsfostersmith.com/produc...m?pcatid=24795
. Just be sure to research the reputation of the vendor(s) you're purchasing from so you minimize the chance of a bad buying experience.