Is there a means of looking up a bank name & branch through Javascript?
Perhaps an external service or an complete data-set that can be hosted internally and accessed through JSON?
You can obtain BSBs from Australian Payment Network and load them into your database.
This is pretty good, but sometimes the list can be a little out of date. Also, the banks may close a branch and remove it from this master list of BSBs. However, transactions to that BSB will continue to work because they do a redirect to the new BSB.