There used to be hystry.com [0] but it isn't functional anymore.

Another workflow, though cumbersome, is: Search for a username on hn.algolia, select "comments" and "past months" as filters, then press enter.

Ex: https://hn.algolia.com/?dateRange=pastMonth&query=nostrademo...

[0] https://news.ycombinator.com/item?id=71827