I'd like a later closed cab one. K's used to do a kit. But I don't think there are any left unbuilt.
In some respects I'm surprised there isn't a decent Met A class 4-4-0T kit produced/available both in 4mm and 7mm scale as they were not exclusive to the Met and District railways. Other companies using them were the LSWR, LNWR and Midland, along some of the Met tanks being sold to other companies after withdrawal.
There is a Met C/SER Q kit available in 7mm scale from SER kits.
One starting point for a Met C would be a SECR H. It would give you the chassis but the biggest issue would be the boiler pitch. It would take a lot of work to build a C/Q from the H but it does give you the tank and bunker flares. It all depends upon how much you want to chop the H body around.
There is 4mm version from Cults3D.com as a downloadable file for printing which may be adapted to fit the H chassis
Metropolitan Railway C class 0-4-4T loco 1/76 scale
Wills used to produce a 4mm H class whitemetal body and nickel silver chassis kit. In reality the SECR H was a direct descendant of the LCDR R and R1 0-4-4T classes rather than the SER/SECR Q and SECR Q1 0-4-4T.
My dad back in the 1960s converted the Hornby Dublo R1 0-6-0T into a SECR (ex SER) Q 0-4-4T - nearly but not quite Metropolitan.
