I'd guess that there isn't enough of a market to make it worth anyone's while to design and manufacture them in quantity. With that style of Pistol the scope rail has to come backwards from the action but it could be made to stand off from the action and be a little bit forward compared to how the plastic item mounts. It could easily be done as a one off, but the finished result might look similar to the plastic part but be made in alloy.
Vic T