Very good explanation. I haven't found a over the counter solution yet.
Can you attach a photo of one? Maybe it’s possible to 3D print it?
The throttle on the GLA is top-hinged unlike other modern MB models and BMW. I don’t know what your Focus had, it was probably the same. I’m not sure if that poses a problem but maybe important to consider.
see if you can find a company locally that can do some 3D modelling and print one for you. Otherwise you could see if the hinge on the pedal itself is adjustable.
This is the first time I’ve ever heard of such a thing and I have no knowledge or experience with it. Please take caution and do sufficient research prior to attempting any of the above thoughts.