There was a project that @einet made a while ago, Anake WHM API, a script that could theoretically help you in making a client. I haven't tested it recently, so I'm not sure if it still works. Other than that, there really isn't any ready-made client that I know of. Btw, this is not related to your question but, I'd suggest you disable CloudFlare on your reseller site, as it will break it.