I too was looking for the brass plug and chain. Found some but they wanted 40.00. no thanks.
It took some time but I came up with a very workable solution.
Now selling these $15.00 plus shipping.
timothyjring at gmail dot com
That plug looks like it could be pretty uncomfortable! I bought this at Home Depot for a buck or so, with a rubber o-ring to fit. Rounded the edges a bit and it works like a charm. No screwdriver needed.