I would use the BJStats.com charts
Didn't know those charts existed, I am going to have to spend some time on that site ;>)
Take the total hands at a particular count number and divide by the total number of blackjacks to get your percentage of blackjacks.
My remark about penetration has to do with the effect of removal of the first card in your hand. With a small number of remaining cards, If your first card is a Ten or Ace, your chances of getting an Ace or Ten has increased by 1/(remaining cards). As (remaining cards) gets smaller, your chances for a blackjack increase.
This is why chances for a blackjack are greater in single deck than in a 6 deck shoe off the top.