alt Hacker NewsAs a professional-level baritone who has sung tenor parts quite a lot, there is a shortage of every low voice type (directors are often conflicted when I make the offer to sing tenor). People who can produce a chorally-acceptable A or Bb are in the shortest supply, though. It's getting worse as the amateur singing circuit gets smaller and the gender ratio gets more skewed.
Amateur-level choirs tend to have a lot more basses than tenors because it is easier to sing bass without effort spent on vocal training.
I am an amateur baritone, in school I was used for tenor parts because of course there was a shortage and I had good enough technique that I could sing tenor parts, if not well. Now, I sing second bass for a men's choir, because that was what they were missing. I think all not in-the-middle voices are scarce.