Specific requirements for certain random encounters?

[Frank Horrigan@BIS]

If there's something that I haven't been able to fully experience while playing Fallout 1, then it's some its localized desert encounters. Encounters near the Khans' location and the Glow have been especially evasive. Most encounters around those areas turn out to be "general ones" (encounters not linked to a specific location), like finding mole rats, radscorpions, etc. The ones that I've never been able to come across are the following:

Khans

Caravan attacked by raiders - here, caravan masters are supposedly carrying "Fuzzy paintings", an item notably only to be found in the crashed flying saucer special encounter. I also recall reading somewhere that there is a luck requirement for this encounter to happen

Lone raider - a raider who the PC can interact with. Upon doing so the raider will share his story on how he became an outcast

The Glow

Radiation hot spot - bring Rad-X

General

Stampede - a brahmin stampede you can come across in desert terrain encounters only


Another thing that has piqued my interest is that - according to the Fallout Wikipedia - Zark, a member of the CoC, should be able to join the PC if he/she is able to convince him to do so. This is perhaps only doable in modified games?

EDIT: I found the answers regarding the encounters while checking some files