There probably is not that large of a market - external skimmers are hard to sell. Large tanks are not all that common.
FWIW - I had a 300 with a RO DC pump and had three pump failures in a year - Coralife got me new pumps, but the last one went out a few months out of warranty... they were good about it. The skimmer did not work all that well either with that pump on any setting, but the lowest setting would pull the most gunk which was kind of a waste of a larger pump. The same body with a Sedra 9000 skimmed twice as much stuff out of the tank. Perhaps the design of the Varios pump in the current models is better.
If you need external and don't mind a big skimmer, then a LifeReef or some sort of Beckett will blow away a needlewheel.