Long story short, I want more spells for my upcoming ACKS game. I'm not interested in building a ton of spells from scratch (I'm looking at you, Stoneskin). What other system is safest to steal from? I'm looking for a system that has spells not in ACKS and is most compatible. Labyrinth Lord AEC? BECMI? AD&D 1E?
two of my favorite products with extra spells (and spellcasting classes, but that may not be relevant here) are "The Crimson Pandect" by Sine Nomine Publishing (http://www.drivethrurpg.com/product/102073/The-Crimson-Pandect-A-Handbook-of-Eldritch-Lore) and "Magical Theorems and Dark Pacts" by Dyson Logos (http://www.drivethrurpg.com/product/115023/Magical-Theorems--Dark-Pacts) .
There's a good deal of overlap with spells already described, but there's also some goodies. If you like the Crimson Pandect, you can buy other books by that publisher in that implied Eastern-ish setting, which includes a lot of spells you may already be familiar with, but slightly tweaked and presented in the same prosaic, vaguely mystical way.