Supervisor password:
A supervisor password (SVP) protects the system
information stored in the IBM BIOS Setup Utility. The SVP
must be entered in order to get access to the IBM BIOS
Setup Utility and make changes to system configuration
settings.
Attention: If the SVP has been forgotten and cannot be
made available to the servicer, there is no service
procedure to reset the password. The system board must
be replaced for a scheduled fee.
FROM:
ftp://ftp.software.ibm.com/pc/pccbbs...df/62p9631.pdf
HOWEVER, if you are willing to pay for someone to provide you with a means of recovering the key, this person claims to do so.
http://www.ja.axxs.net/unlock/key_for_t20.htm
I do NOT recommend doing that. In fact it may be cheapest to buy another computer as going rate seems to be $125.00 to $150.00 for EACH recovered password.
I hope someone is more lucky than I am in finding what your looking for I couldnt find any mainboards by them selves.
If you are unable to find anything otherwise

Below is a link to ebay for several laptops. You might consider them, just be careful.
Ebay IBM T20 LAPTOPS