Reddit reviews SF Cable, Keyboard PS2 to AT Adapter (6 inch); Din5 Male to MiniDin6 Female

https://www.amazon.com/SF-Cable-Keyboard-Adapter-MiniDin6/dp/B0016RTMQE/ref=pd_sim_147_4?_encoding=UTF8&pd_rd_i=B0016RTMQE&pd_rd_r=VY3M2AB53BW3H8N6DWF9&pd_rd_w=HmuUZ&pd_rd_wg=LFrAf&psc=1&refRID=VY3M2AB53BW3H8N6DWF9

To convert to PS/2 then a PS/2 Female to USB Male Adapter

I've actually seen and used that setup before.

There is a PS/2 connector next to the DB-25 serial port. It will only work with a mouse. If you open up the case you should find that top slot isn't actually a PCI or ISA card, but a specialized riser card designed for that motherboard.

For the keyboard, you will need an adapter that lets you plug a PS/2 keyboard into the AT connector (found just above the DB-25 serial port). It's a cheap and simple electrical adapter as the protocal is 100% compatable with PS/2, looks like you can still find them on amazon.

Convert the DIN-5 plug on the keyboard to PS/2 with this:

https://www.amazon.com/SF-Cable-Keyboard-Adapter-MiniDin6/dp/B0016RTMQE

And then convert the PS/2 to USB with an active PS/2 to USB converter like this:

https://www.amazon.com/Monoprice-Keyboard-Converter-Adapter-110934/dp/B00IACID2C/

You can get a PS/2 keyboard (WASD V2 supports both PS/2 as well as USB, for example). AT connector and PS/2 are the same protocol electrically, just different connector. You need something like: https://www.amazon.com/SF-Cable-Keyboard-Adapter-MiniDin6/dp/B0016RTMQE

If you want to build a keyboard that talks the PS/2 serial protocol, it is possible, but you'll need to write your own firmware.

As for the 486 keyboard adapter, the larger old AT connector is compatible with the smaller and newer PS/2 keyboard connector. Adapters are available in most of the usual places for about $6.

https://www.amazon.com/SF-Cable-Female-Din5-Keyboard/dp/B0016RTMQE/

ISA sound blaster card I would recommend eBay. If you want a genuine ISA sound blaster, you can go with pretty much any of them from the original 8-bit all the way to an AWE64 model. Prices will vary based on type and model. Perhaps around $20 shipped. If you don't need an actual sound blaster but are good with any number of the clones, those will probably be much cheaper.

The same thing will be true for an ADB keyboard and mouse. Ebay would be my recommendation, or perhaps craigslist. Perhaps around $25 + S&H.

A good tip, if you're not familiar with it, is to check the 'sold' listings on eBay. Those will give you a good idea how much something is worth before you go bidding on it or buying it on craigslist.

That's only going to work if the motherboard has a header for it, and since it has a DIN port, I'm guessing it doesn't. You're going to need this for the keyboard, and a serial mouse.

The easiest way to get a modern keyboard on this machine is to use a DIN to PS2 adapter, like this:
https://www.amazon.com/SF-Cable-Keyboard-Adapter-MiniDin6/dp/B0016RTMQE/