The BBNCTransactions table is not available to The Raiser's Edge API for access.  However, the PluginService/MasterService.asmx installed with Blackbaud NetCommunity does contain methods that can be used to access information stored in The Raiser's Edge about BBNC transactions.  

For more information on how to use the PluginService, please see the Blackbaud Developer's Network as well as the BBNC Community