The Global Philatelic Network handled all of the Erivan collection with auctions across a number of locations over the years. The H.R.Harmer branch carried the U.S. parts.
In this last catalog, these two pages were up front:


Note that the phone numbers of the principals of the company are all in Europe. I would not expect there to be a "robust" American presence in the near future, though I would love to be proven wrong. Would be great if the market could handle more players.