In Chapter 1 there are 5 such Archers, but you are unlikely to run into them, unless you are very adventurous. (You may meet them later, in Chapters 2, 3 or 6.)

In Chapter 2 the maximum number of Poison Archers is 7, but you may already have killed 5 of them in Chapter 1. If you haven't, you will probably encounter 3 of these. The remaining 2 are hard to find. (One can only be encountered in Chapter 2, but the other one remains until Chapter 6.)

In Chapter 3 the maximum number of Poison Archers is 14, but you may have killed 6 of them in Chapters 1 and 2. If not, you are unlikely to meet them, unless you have an urge to travel. Out of the remaining 8, you are quite likely to run into 5, as you go North (3 in this Chapter only); but the remaining 3 won't be met with, unless you go the other way (in this Chapter only).

Chapter 4 has 46 Poison Archers !

Chapter 5 has 13 Poison Archers .

In Chapter 6 you can encounter 4 Poison Archers carried over from previous Chapters (1, 2, 3), if they're still alive. In addition this Chapter has 45 additional Poison Archers , specific to this Chapter. So look out!

Chapter 7 has 18 Poison Archers (and all their Quarrels are either Tsurani or Elven).