I go to local performances of baroque-era and somewhat earlier music regularly. I have noticed on occasion in a small vocal performance that has 2 people per part, occasionally a female contralto is paired with a male tenor. (I don’t know enough to know how that works as far as needing to modify the original parts or not.)

Though conversely I’ve also seen a male countertenor paired with a female alto, so maybe it’s just generally “who’s available for this performance” rather than an issue with a general shortage.