Quick Update!
We've spoken with Westone but sadly they're not interested in offering it directly. A few different vendors approached us with pricing but nothing good enough for a drop.
We'll keep looking (the 4R would be a great product) but this isn't a feasible item right now.
i've been using the 4xx series from Shure for a while now and i'm loving them! it would be great to be able to move to the 5xx series (TWO bass drivers).