If the prior preparer is a CPA, under some states ethic's rules, you may be able to request the prior accountant provide data on the client in "electronic format which is usable". At least in my state the prior accountant can charge for providing the files, but there are limit's, IE the charge needs to be reasonable to the time required.

Generally I have client's sign a form authorizing the prior accountant to provide me any thing I request. In this case I would request the proseries data files.

I do ask the prior accountant that if there are any charges, for an estimate of the charges and to please bill them direct to me. Most don't bother but a few do.