For some spells, like Darkvision, no one else can cast permanency on you to make the effect last until dispelled*. So for non-caster's there's no way to permanently get that… unless you can find a way to use someone else's caster level while casting a spell, such as when reading a scroll.
*Permanency makes the duration of certain other spells permanent. You first cast the desired spell and then follow it with the permanency spell.
Depending on the spell, you must be of a minimum caster level and must expend a specific gp value of diamond dust as a material component.
You can make the following spells permanent in regard to yourself. You cannot cast these spells on other creatures. This application of permanency can be dispelled only by a caster of higher level than you were when you cast the spell.
Can there be a scroll of permanency? – Yes, according to Ernir, but the cost (both for CL and diamond dust) would depend on what you intend to make permanent with it, thus it would be a very specific item.
However, once you get it: When using UMD to successfully cast it, while under the influence of a spell that's to be made permanent, will that work?
Best Answer
Yes, such a scroll can exist, but it's a rather specific item.
When a spell refers to "your caster level", it is the caster level at which the spell is cast, rather than the caster level as it would be generally calculated from the caster's classes. The "you must be of a minimum caster level" clause is not a problem for scroll-casters, its meaning then just translates to "the scroll must be of a minimum caster level" (read: you would need a CL 10 scroll of Permanency to apply it to Darkvision).
Likewise, the "in regard to yourself" clause refers to the caster, which would be the user of the scroll rather than its creator.
However, it is not sufficient for the scroll's user to be in possession of the diamond dust, as material components of scroll spells must be supplied at the time of crafting. So to make a scroll of Permanency that can make a Darkvision spell permanent, you would need a CL 10 scroll that has the 5000gp material component built in as part of its creation process.