My pdoc put me on SAM-e for ADHD when I could no longer tolerate adderall. It worked pretty well but not as well as Adderall, obvs. You can get SAM-e at any store that carries vitamins and supplements; it's a natural substance your body already makes. Don't take it late in the afternoon though, you can get some serious insomnia. The ideal dose in studies was 1600mg but I could never get that high. I took 800mg a day and it worked.
Also there's some evidence that people with ADD have low zinc levels so zinc supplements are sometimes recommended. Fish oil/krill oil you want at least 500mg in each pill of EPA and DHA; i forget which affects cognitive but studies show that to get a cognitive effect you need to take 2-3 grams per day.

oh yeah and I don't think any of these are homeopathic but maybe they'll help you.