You get the tax number from the IRS (Internal revenue Service). All of their forms can be down loaded from their web site.

My local bank will provide the forms necessary to apply for a tax number. It surpries me that any bank can't do that. I think maybe you spoke to a low level clerk who just didn't know how, because it isn't a thing they do often.. Try asking the bank manager.

At any rate, if the bank won't do it, simply apply directly to the IRS.