Mark,
Try this link: **LINK**
If you go direct to the website you will need to select GB. They don't market to model engineers, but they often supply toolmakers etc. so are happy to deal with very small orders and my local one has a good stock of useful offcuts at <1/2 normal price. They even have a 'model engineers corner' of modest sized lighter offcut sections in the office.
I can't see the size you want but they have a bewildering array of flats in EN3 (but far fewer in EN1A).
For the metric doomsayers of the 1980s and before, I point out they have more imperial than metric sizes as well as using EN numbers 
Neil