I've got a couple questions about mercenaries someone may be able to help me with.

1) I've noticed I'll have mercenaries show up a lot in some of my provinces and never in others. I've heard that they prefer more undeveloped lands, especially if it doesn't have a keep yet, but are there any other factors that influence their preference? Are some provinces just naturally more likely to attract mercenaries than others?

2) My mercenary market always seems to dry up right when I need them. One year I've got like 20 merc options just waiting to be bought, and then the next year I get attacked unexpectedly and I could actually use a little temporary help, and what do you know! All I've got to choose from is two trebuchets and an archer unit! Seems like those lily-livered swords-for-hire heard there was a war on took to the hills. Does this happen to everyone else, too, or do I just have extra cowardly mercenaries?