Oh boy, where do I begin? For me, I begin my rant of hard to find parts with anything made by IBM, including but not limited to the following:
Hercules Graphics Card/Plus/In Color (not IBM but nothing else is so close)
Monochrome Display and Printer Adapter
Color Graphics Adapter
Enhanced Graphics Adapter (especially fully upgraded w/256KB)
PS/2 Display Adapter (IBM's 8-bit ISA VGA card, no one's ever seen it.)
IBM PC 5150 (16-64KB board)
IBM PC/XT 5160 (esp. last BIOS w/640KB)
IBM PC/XT Model 286 5162
IBM PC AT 5170 (esp. w/Enhanced 101 Keyboard w/AT interface)
IBM PC Convertible 5140 (w/supertwist or backlit LCD)
IBM 5161 Expansion Chassis (w/extention and receive cards + cable)
Asychronous Communications Adapter (serial card)
Printer Adapter (parallel card)
Game Control Adapter (gameport card)
160/180KB Full Height Floppy (used in first PCs)
Half-Height 360KB/720KB/1.2MB/1.44MB Drives
External 360KB/720KB Drives (from IBM)
5144 Convertible Monochrome Display
5145 Convertible Color Display
5151 Monochrome Display
5153 Color Display
5154 Enhanced Display
NEC V-20 (8088 upgrade)
8087 Math Coprocessor
80287 Math Coprocessor
Convertible 256KB Memory Upgrade (IBM brand hard to come by)
2MB Expanded Memory Adapter
512KB-6MB Memory Expansion (for AT or XT/286)
Technical Reference Manuals (esp. covering later models of PC, XT, AT or Options and Adapters.)
But let us continue to Sound Cards and Devices, try finding some of these:
IBM Music Feature Adapter + Midi Breakout Box (can use two)
Roland CM-32L, CM-64 or CM-500
Roland LAPC-I
Roland SCC-1A/B (more sounds than older SCC-1)
Roland SCD-15 (MPU-401/AT + SCB-55 on one, SCC-2 in essence)
Roland MIF-IPC (first MPU interface with breakout box, only works in PCs and XTs.)
Roland MPU-IPC/MPU-IPC-T/MPU-IMC (with breakout boxes)
Creative Music System/Game Blaster
Creative Sound Blaster 1.0-2.01 (w/CMS chips, try finding a 2.0 with them!)
Creative Sound Blaster Pro/Pro 2
Creative Sound Blaster 16 (w/ASP/CSP chip)
Creative Sound Blaster AWE64 Gold (w/Upgrade Modules)
Gravis Ultrasound /MAX/ACE/Extreme/PnP
Covox Sppech Thing
Covox Sound Master
Innovation SSI-2001 (debatable whether it even exists)
Adlib Gold 1000/2000
Yamaha SW60XG (DB-50XG on ISA board)