Try T-J Model Trains in Pasco, Washington.  Teressa and Joel maintain a much fuller catalog of in-stock detail parts than I have been able to find elsewhere.  They have an eBay store, but can also be ordered from directly.  Teressa is often busy home-schooling their younger 7 kids, but the older ones maintain the store.  I think they recently bought Precision Scale(?), lock, stock and barrel.

-- John