Is it possible to export a list of the tax-line mapping accounts? I'd like to send it to our tax accountant so he can help me map my chart of account items.

You have this in Reports menu > List reports, Account List. View that report and customize it and the reports have Export as Excel or Save as PDF, at the top.

You only need to do this if your Tax Preparer plans to Import the QB data file into their Intuit Tax Prep program. That is the Only reason for maintaining this function = links two programs together.