Does anyone know where there is an existing script that will solve amortization needs? There are several simple ones that accommodate the standard US amortization method. But, banks use 360/365/actual days and other methods to calculate loan amorts that are different from the standard home loan amort. anything out there?

A couple of things.

Check legislation in your locality. That may dictate the exact calculation. In Ontario here is legislated at compounded semi annually and not in advance even though payments are monthly.

Way back when the earth was green and I was doing appraisals, there used to be an appraisal institute publication, six functions of a dollar that gave the exact Canadian calcs. Check with your local appraiser Community for a similar publication or alternatively, for their exams, se exactly what functions they are using on their "approved" financial calculator.

HTH