Small, 80yr old design classic

I've been after one of these for years and finally got the opportunity...I am now the very proud owner of an original 1933 London Transport Underground Railways of London map by H. C. Beck.

It's the Third card folder edition, published in September 1933. It has a few modifications from the First Edition published in January 1933. Principally, the interchange symbols are now open circles instead of diamonds. There is also some smoothing of the original kink in the District Line near Ealing Broadway and 'London Transport' has been added to the bullseye (later termed Roundel). A new escalator connection had by now been added between Bank and monument stations and a large red notice added to the map this effect. The front cover no longer says 'A new design for an old map'.

Now...where can I find that elusive First Edition?...(if anyone has one they want to sell, feel free to contact me!)