I think your best bet is to check out what the continental kit makers have to offer - Faller, Pola, Vollmer, Kibri, etc. especially if you want a continental flavoured viaduct like the RhB photo you've referenced. The RhB is exceedingly popular as a model influence, so someone may have something to suit.
I don't know how difficult it would be to scratchbuild some like this since I don't know whether the arches themselves are wider on the outside than the inside, and if they are, how the brickwork on the inside of the arches is laid.
David