It is very difficult to find separate 386-class components, so it may be easier to get a couple of abandoned 386 boxes and build a new one from the parts. The best for this purpose are taiwanese "Yum Cha" noname components. Brand name boxes may be more robust, but usually are incompatible with everything else (there were not many hardware standards back in 1990).
CPU:
The socketed ceramic version of the 386 is the the preferred choice, because the plastic encased 386 CPUs most likely are the 386SX variant, which only has a 16bit external data bus and performs not much better than a fast 286. The best would be an AMD 386DX-40, but that one may be rare and hard to find in Australia. Next would be an Intel 386DX-33, with a bit of luck (and a heatsink) you can run it at 40MHz.
Mainboard
If you find a 386 mainboard, you'll have to check for a few things:
- Capability of running a 40MHz processor bus speed
- Onboard L2 cache (usually 32-128Kb)
- Five or more 16bit ISA slots (you will need those)
- Decent amount of SIMM sockets (4 is standard, 8 or more would be perfect)
- Exchangeable CMOS battery. Beware of "Dallas" CMOS chips, because they have a battery that cannot be replaced easily and is usually dead after 15 years.
RAM
386 mainboards usually take standard 30pin SIMM modules. On 386DX systems you will always have to fill 4 sockets (1 bank) with the same type of memory module. The most available size is 1MB per module (4MB is rare and expensive, 2MB impossible to find).
The maximum amount of memory supported on standard boards is 16MB. For a 40MHz system you will need 60ns modules. 70ns modules will run either unstable or much slower because of waitstates.
Storage controllers and I/O
The best option would be a multi-I/O IDE controller card. These can be found everywhere and feature a floppy drive controller, a IDE controller (2 channels), 2 serial ports, parallel port and sometimes a gameport. Maximum supported hard disk size is 504MB.
Video card
Get a Tseng ET4000. It's the fastest on the ISA bus and very compatible. Special "accelerator cards" may be faster in Windows 3.1, but are a real pain when running DOS games. Same goes for the infamous Trident and OAK VGA cards.
Sound card
For the best game compatibility get a SoundBlaster Pro/16. A Gravis UltraSound is also cool for games that support it.
Building a working 386 box is not easy, but is surely worth it, especially for games from the late eighties and early nineties. Good luck!