I reviewed the service manual and our part supply store, and it looks like the "Ink System Assembly" is one part that includes the cartridge chambers, ink lines and "ink selector" unit (whole unit containing dampers). This part costs about $170 plus shipping (from CompassMicro.com, where we get any part we don't carry ourselves). We did get 3800/3880 dampers, as well as 7900/9900/7890/9890 dampers from the supplier where we get all our other dampers, but after reviewing the parts list and service manuals, it looks like those parts are whole units and not generally replaced individually (though from wheat I've read- CAN be done, but its quicker/easier to replace the whole unit).
After cleaning the capping station and bottom of the print head, you can soak the caping station with PiezoFlush, then move the print head over to soak overnight. This can help clean the print head, though will not resolve any issues that may be further up the ink system (like inside the dampers or ink lines). To clean the internal system, your best bet would be to install the set of flush carts and do 3-4 Power Clean Cycles. Print a nozzle check to see how things look, and if it's not perfect- turn the printer off overnight to let the Piezo Flush do it's thing, then in the morning do a regular cleaning cycle and print another nozzle check to see if there's improvement. If the nozzle check looks the same as before, then you can try letting it sit longer, or begin looking into replacing the dampers/ink system assy.
I will check our 3800 upstairs to refresh my memory as to where the wiper blade is and how to clean it.