Have I made you want one? You can buy a brand-new Model M keyboard, made from the original IBM design, and even using the original IBM molds. They're made by Unicomp in Lexington, Kentucky, USA using the original IBM equipment. There's one specifically for Mac computers, too. They cost $80 to $120 plus shipping.
Not convinced that you should pay a hundred bucks for a keyboard? It will make your life and work easier, and it'll last forever. Computers may come and computers may go, but your Model M keyboard will go on and on. Read what NPR's Martin Kaste has to say about it.
Using an Older Model MIf you're lucky, as I am, you have an original Model M keyboard. You also have a problem; the keyboard has a PS/2 type plug, and modern computers do not have PS/2 sockets! (New Model Ms from Unicomp come with a USB interface.)
You will need a PS/2 Keyboard To USB Adapter. Cheaply made "bulge in the cable" adapters do not work. Use the link to get the right thing. (Disclosure: Amazon pays me a few cents if you buy using the link. I'm almost up to a dollar a month in commissions.) You will probably also need a short USB extension cable because the adapter is too fat to plug directly into many USB sockets. Plug directly into the computer or into a powered USB hub; an unpowered hub will not work because of the power requirements of the keyboard.
Cleaning up that Model M, and USB ConversionIf you're like me, after a couple of decades enough glop has dropped into your keyboard to be truly disgusting. The nice people at Unicomp will clean and thoroughly test your keyboard for $30 plus shipping. Email them at email@example.com for an RMA number. When you have the RMA number, order a Class 1 keyboard repair and ship your keyboard off to them. (They can do more extensive repairs in the unlikely event that you have a non-working keyboard, but it might be better just to buy a new one from them.)
For a little extra, Unicomp will make the USB conversion for you. If you're going to send your keyboard in for cleanup, order the USB conversion, too. That's far better, and possibly less expensive, than using an adapter. (It was $10 when I had mine done; that's less than the price of the adapter. Check with Unicomp for the current price.)
Converting the Keyboard to USB YourselfSome people, handy with soldering irons, have installed the USB adapter inside the keyboard case. The idea is attractive to me because the adapter hanging from a cable on my laptop dock is un-aesthetic. I haven't tried it, but it might not be hard to do. A little time with Google should find some help.
But really, just get Unicomp to do it for you. They're the professionals.
The IBM Model M Keyboard and Modern Computers by Bob Brown is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.