The Model M, well, I'm not sure I want an old keyboard, just one that has the old look.
If they weren't out of stock on just about everything, you could get a new one from unicomp.
http://pckeyboard.com/page/UKBD/UNI041A (101-key like the model M)
http://pckeyboard.com/page/UKBD/UNI044A (104-key with a windows and menu key)
There are other models, this is just an example.
Since there is no real "old school aesthetic", I must assume you mean the classic beige style that IBM seems to have liked in the 1980's. I have old school keyboards from the 1970's that feature nice grey/white keycaps, and there are tons of old keyboards that just have a grey case and one colour for the keycaps (see all the ancient HP 'boards from the 1960's and 1970's for example)
Still, there are keyboards that perpetuate this style. Old cherry terminal keyboards, IBM model M's (I must say, many used model M's are still quite sturdy!) even newer ones from cherry and ducky can be good. If you don't like the durability of the PCB-mount cherry, you can look into making a plate for them. If you don't like the case colour of some ducky's (I must say, those PBT dyesub keycaps look great!) you can paint it. There is a way around every obstacle.
WYSE is an option, but it's more of a beige and blue instead of beige with black printing. Also, the function keys are all the same. Up to you, of course.
I would recommend the unicomp. It's a very similar colour (if not, the same) to the old model M's and model F's that have popularized the trend, and it' has a similar construction and (one would hope) durability. It's also not too expensive and can be had in USB. The main downside is that it's only got 2KRO like most membrane keyboards.
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Edit: you can also get them in euro layout. The floss mod seems to be popular to help with the sound.
