Look, that you got the speedy with the recessed subdials ... will be not easy to find, I'd tried it too ...
The diameter of the plexi is written on the package ... 340 ... means 34,0 mm
I think there is no moony with plexi ...
Get the handwind, switch of the glass, look for the diameter (something 35,xx mm) and buy this plexi at cousinsuk.com ... will cost you somthing about € 3,00 + PP