I'm in chapter 10 (stupid witch 4 armed boss - green) and was wondering if it's too late to acquire the purple rune. Heard someone say it's back in Lindseys chapter. Was that my only hope for it, or can I get in another way?

not really sure but, if the game let you through without it, then you proabably dont need it. Just a guess.

wow i got that one easy.
you have to be the edward lindsey guy.
in the temple that he explores he gets to a level where there are three alters that are protected by damage feilds u must dispel all of these fields. every time u dispel on of the fields the screen will show u a wall that is protected by a purple field. once u have dispelled all three the purple fields will vanish leaving a small hole.
from here u have to find gold necklace and braclet to open the door to the lower levels. once u have done that u can get the rest to the runes on this level that u need.
after u get the runes u will also find a spell scroll teahing u the summon trapper spell. run back upstairs to the hole in the wall that u found and summon the trapper and control him to go inside the hole. once in side u will find 2 horrors and a swicth. step on the swicth and a door will open (get ready to be attacked by one of the horrors in the hallway) after u beat him the go inside and (get ready to be attacked by the other horror inside that room)pick up the purple rune.
sorry i dont remember the true names by heart (im at work while typing this) but the summon trapper spell is a 3 point spell with summon and creature runes

well thats is i hope is helps

the runs are

tier (summon)
aretak (creature)
and an alignment

when you get the L5 circle of power add 2 pargon (power) and you'll get summon zombie, add 2 more pargons when you get a L7 circle of power and you'll get summon horror