My Kings Ferry Ithaca’s use Winchokes, but my guns are/were 12 gauges. I ordered my extra chokes from Trulock.
I believe the kings ferry 20 gauges still used Tru-choke threads/chokes.
These are available from Trulock as well.

The Sandusky guns use invector plus threads but the bores on the Sandusky guns are not overbored like Browning inventor plus barrels.