The other shops mentioned are both very good, but not close to any river.
"Any other good multi scale train stores in the Philly/Del area to check out?"
(No river proximity mentioned with second inquiry of ("...other good...").
Also, Doug's Trains on Philadelphia Pike in Claymont, DE. Small store but has a wide variety of speciality tools, blades, drills, adhesives, fasteners, wood & brass shapes and new & used O gauge track plus the latest OGR in the magazine rack. Heavy stock of HO brass. Bonus, it's only a half mile from the Delaware River.