We don't generally sell transformer spares, especially if that happens to be the only piece that might be an impediment to building kit clones (not that this is at all what you're intending to do).
When a transformer is discontinued, we keep a few spares sitting around. Humorously enough, if you ordered a PT-5 on the parts page, that particular transformer is NLA (though our PT-11 functions in its place).
If you happened to need a replacement transformer way down the road and we do not have spares, there are winders who can whip out a one-off, and we could provide the specs to help get that done.
Typically we would expect a power transformer to die from excessive current draw, which in the Moreplay would pretty much have to come from failing power supply caps. These are likely to last ~30 years and the fuse provided should open up long before the high voltage secondary winding would overheat, so there's not a huge concern there.