Quinine works and is less expensive but has some drawbacks. These include a smaller margin between efficacy and safety, the requirement for daily water changes, and probably it is less effective.
Chloroquine is dosed once and remove in one month by carbon.
Places to find chloroquine:
In the US, your neighborhood pharmacy or an online Canadian one. Both require a prescription. In UK no script is required.
You could go to your local vet who could issue a script and sell it to you.
You could email Louis at a vet pharmacy I now use. They have a vet on staff that issues the script. Pm me for info.
Or you could buy bulk at fish chemical dot com. What they sell will treat 25,000 gallons and for some reason they don't seem to require a script.