I remember getting a lightning bolt scroll in Act 1 btw. It's definitely not that rare.
Its actually super rare if you never bought one in act 1 because vendor loot scales with your character level.
In Act 3 and at level 12, no vendor sells scrolls below level 5. So yes lower level scrolls are the rarest in the game.
I've never come across either a lightning bolt or longstrider scroll at any vendor by the point I realized I wanted to add those spells.
I've looted every pile of books / scroll stack / everything that can be looted. I had 5 chain lightning scrolls and 0 lightning bolt and longstrider scrolls.
As it does turn out, relying on memorizing scrolls necessitates planning to buy all the spell scrolls from the start of the game. If you didn't do that, before act 3 you will no longer have access to purchasing level 1-4 scrolls from vendors.
On the other hand, there are definitely multiclass combinations relying on the Wizard spell scribing that are worth losing one feat for, e.g. Tempest Cleric.
That is exactly the build that people are mentioning, and it works even better with 8 sorc levels too, so long as you remembered to buy a lightning bolt scroll in act 1 because after that you will never find one again.
I'd suggest people load up a level 12 act 3 save and try to make their 2 level wizard multiclass there, and feel free to tell me exactly where you manage to find all the scrolls you need.
