According to Anthony Roberts, 100mcg T4 during a course of GH is beneficial. How true this is, I don't know. But it certainly doesn't hurt. I get my T4 tabs from India, as there are no board sources that I know of that sell it.
T4 is very easy to get where I am, they sell it over the counter. Pm me if you like and maybe I can help you out one way or another. Im not a seller though. I will always prefer t3 over t4