I'm not sure if you can find them where you live, but depending on where you are you might be able to find them on Amazon or Ebay, check out out Ocean Free's line of special Arowana meds:
Imho OF knows Arowana better than most other medical product suppliers -- simply because of the fact that their main company, Qian Hu, is one of Singapore's oldest Arowana farms around since the 1970's, and unlike other co's they have easy access to plenty of Aros to test and then orientate their products.
I honestly don't know which of this line would be best for your Aro's condition, so I would highly advise to drop them a line (best via Facebook message, you'll get a pretty quick response:
https://www.facebook.com/QianHuAccessories/ -- and they're quite helpful).
For the record I have absolutely no relationship with OF/Qian Hu except as a consumer; and one thing to mention is that their Aro meds aren't super cheap, esp. if you're treating a larger tank.
All of that said, if your Aro really has HITH (which I personally cannot tell from your pix -- how about it's feces, are they white and stringy?), that's quite serious and needs to be acted against asap -- most popular is using something like Metronidazole (best fed orally via soaking in food but if your fish isn't eating you can still dose by adding directly to water, just less effective).
However, @RD has a great post about HITH and treatment via epsom salts, highly recommended reading:
https://www.monsterfishkeepers.com/forums/threads/treating-hexamita-aka-spironucleus.339362/
It's in the Flowerhorn section but info would still be applicable to any fish I'd reckon.
But hopefully RD will chime in himself, he knows WAY more about this stuff.
Best of luck and hope your Aro recovers soon!