FamilySearch has a very large collection of Pennsylvania probate records, including, it claims, more than three million images, although unfortunately very few of these have been indexed.
The same images are available on Ancestry, where most of the wills and probate records have also not been indexed. However at least some of the indexes to the wills have been which may help. For example, I was looking for the will of a James Miller who died c 1749. An Ancestry search took me to this will index, which shows that the will is in Lancaster County will book A, p 168, which is on Ancestry and on FamilySearch.
Some books of abstracts of Pennsylvania wills published by the Genealogical Society of Pennsylvania, some available on Archive.org.
Many of the Pennsylvania county governments also make their will indexes available on their web sites.
