I am currently in the process and will be adding a tutorial on this.
What type of function do you want the switch for?
The switch that I found that will fit the hole exactly comes from a 1999 thru 2001 Galant. You can easily find them on Ebay for around $10. They don't have to be imported from Japan. My parts guy also found switches from the Endevor fit also part number (MR962421). They are around $20 brand new. The issue with the switches on the Endevor are that the wire will need to be soldered to the connectors on the switch.
Another thing to remember on using these types of switches is that they are (Latched On/Off Output Using a Single Momentary Pulse). Meaning that the computer(ETACS-ECU) controls the function of the switches and is routed through a relay system. To avoid connecting and having the computer control the switch function I used the relay system. Last week I have built the relay setup and will post pictures in the near future. The relay setup parts cost around $22. I haven't been able to find this setup for sale on line, that is why I built the relay setup.
You can check out the link JSRD posted on removing the blanks next to the ASC switch. Any questions that I can help with leme know.