[ister]

Big spoilers on scroll counts and locations
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Stoneskins: One in the Hand. One in ToTLM. That's it.

Mirror Image: Orrick has 3 if you buy one before each inventory change. There is one in DE and one in HOW

Blur: Orrick has one, and there is one in HOW

Invisibility: One in Vale of Shadows, one in HOW.

Tenser's: One in LLD, 2 in TOTLM

I think you ought to look more at improved invisibility rather than invisibility as your uber backstab spell. As far as I know there is only ONE copy of that spell. It allows you to backstab, then move away from the target, while still invisible and backstab again. It also prevents you from being targetted by spells. It's a great spell, particularly for your FMT. Of course you can always have the bard cast it on the FMT, so it's not as critical that you give it to the right caster.

On Aerich's points, Orrick has 3 Chromatic orbs and 3 acid arrows, so you should be able to give those to everyone. He also has 3 color sprays (which I rarely use, but which is obviously much better on Insane than on my usual hard). As far as I know there is only 1 copy of Vampiric Touch. There are two cone of cold scrolls, but one is in HOW. Same for Force Missiles and all the shadow monster spells.

Aerich, I think you mean "Shades" as a spell that works better with level, not "Summon Shadows". For "Summon Shadows" only the duration improves with level.