Around here, dried Epazote along with other authentic Mexican ingredients are readily available at our local WalMart. Probably because we do have a relatively large Hispanic population here.
I can't believe you can't find a source by doing a websearch - it's really very commonly available. In addition, although it does reseed heavily & can become invasive, it's extremely easy to grow, & the fresh is 100 times better than the dried. I find the dried relatively worthless.