support for ancient peripherals

["Kleene, Steven (kleenesj)" <kleenesj@UCMAIL.UC.EDU>]

As you might understand, I'd like to replace my desktop, a 2006 Pentium 4
with a 3-GHz processor.  It has always run Debian, and so will the new one.

My concern is about support for three ancient peripherals that I like better
than the modern equivalents:
1. A Northgate Omnikey 101 keyboard (from 2006) with a 5-pin DIN cable,
currently going via an adapter to a PS/2 port in the desktop;
2. A Logitech M-MD15L three-button roller-ball serial mouse (from 2006); and
3. An HP LaserJet 5MP printer from 1995 with a parallel-port connector.

Are desktops still available with PS/2, serial, or parallel ports?  If not,
can these all be adapted to USB?  Are USB-A ports still common, or is USB-C
taking over?  My question is of course not just about hardware but about
software support for these devices in Debian.  They all work now in Buster
(oldstable).  Thanks.