I couldn't find the Ferroli wireless thermostat either, but recently purchased a Towerstat RF/BM wireless thermostat instead. The box said it's compatible with the Optimax 25, but it works in my Optima 701 with no problems at all (despite the manual saying that boilers with a metal cover over the control might have problems with signal interference). Only about £60 on eBay and very easy to fit (no wiring in, just a few spade connectors).
Andy
April 2009