The Model M was made in the 80’s to mid 90’s I believe. We have some in our labs at work on some of the older hardware we support. They’re very heavy and use springs underneath the keys instead of that rubbery pad common on new keyboards.
You can still buy old Model M keyboards from Ebay and such but they are ps/2 and i’ve read that some people have had issues using a ps/2to usb adapter.
Are there any companies still building heavy duty Model M style USB keyboards? I want one.
Unicomp holds the buckling spring patent and manufactures boards. There are better switches out there now like, like the various Cherry MX switches and Topres. The new ones are smoother, but with that crisp mechanical feel. Don’t get a Model M clone.
The Das Keyboard was made for Model M fans. Never used one, but I know some folks who have and rather like 'em. Their famous model also lacks markings for the keys, but their professional model is more conventional.
I use several unicomp keyboards and they work fine. They are not built as well as the original IBM, not nearly as heavy and the keycaps are not (easily) replaceable. But the feel of the keypress is close, so you should like them. Here’s a link: http://pckeyboards.stores.yahoo.net/
I have a couple of Model M’s and a Unicomp keyboard. The Unicomp sounds the same but I found the key resistance to be a little higher than the Model M’s and it put a slight strain on my wrists. I can verify that the ps2-USB converters have a problem and about twice a day my Model M goes wonky for about 2 seconds. I have not tried any of the other Model M replacements.