replacing the deck mounted mast step

i actually have a 1979 contessa 28 (sorry!) but the mast step looks to be the same as that on the contessa 26. Mine has corroded and cracked and needs replacing. i removed the compression post below in hopes of revealing the nuts on the bolts that hold the mast step in place, but they are apparently buried in the glass. i have since then cut away the old mast step with a grinder and now i'm looking for where i can get a replacement. any ideas?
thanks