You could try the main dealer. I broke my 8G VR-4 one and was surprised at how cheap it was from them. About 10GBP!
Part number is MD312865, and according to ASA, is the same part as used on the HSGR, SSG (N23WG version), Super Open Gear, X3, and also the Eclipse and the Chariot Resort Runner GT and GT-V.
I asked on the Evo 123 FB group and it seems that the stock dipstick is about 5mm longer.