These are defined in the Federal and State Tax Reporting as you go through the Wizard.  After it shows you the State Taxes, you should get a window that pops up asking you to define the Special State or Local Tax Items.  It gives you the Internal name you used in the Tax Profile and you select the Tax Type.   I do not know of anywhere in Sage 100 that defines these other than here.  Aatrix may be able to answer this differently since they probably have the codes that are universal.

I setup both Russell City and Russell CO for KY and the screen let me choose the RCRIW for the Russell CO Regular IT withholding and RCRIW2 for the Russell CT Regular IT Withholding.