There are only three differences between Major and Minor Skills:
1) Major Skills start at level 25, Minor Skills start at level 5
2) Major Skills level up slightly faster
3) Leveling up your Major Skills leads to level increases. Leveling up Minor Skills only increases your Attribute Bonuses at level up, they don't count toward leveling up.
You have to train up your Illusion Skill, but you DON"T Have to have it as a Major Skill. It can be a minor skill and work the same way.
The only requirement to be able to place a Chameleon Enchantment on any wearable item is the ability to cast a Chameleon Spell. As long as you have ANY spell (and you can cast it) that grants the Chameleon Effect, you can enchant any wearable item.
Try joining the Dark Brotherhood. If I remember correctly, the Spell Merchant in the Sanctuary has a cheap Chameleon Spell (it may be Night-Eye, I'm not sure)