Lanefan
Victoria Rules
Official? I don't know of any...and there might be some good reasons for that, see below.Just out of curiosity, are there any official sources on the "expected magic item curve"?

Well, part of it is that the magic items in treasure hoards are sometimes determined randomly; meaning there's no way of knowing what a party might find. Further, 1e expects a higher turnover of characters thus there's no way of knowing in advance who is going to find what treasure (example: as DM writing an adventure ahead of time, you put an Illusionist's spell book in a hoard in hopes of boosting the currently-weak PC Illusionist; but by the time the party get there that Illusionist is long since dead and the player is now running a Cleric, and so the spellbook just gets sold off).When trying to grok TSR eta D&D, people tend to say that characters are supposed to progress via magic items (because class features are more sparse), but they never mention what kind of items or in which order they're supposed to get. I know that "game balance" is less of a concern with Old-School D&D, but surely there were some guidelines, and the "+1 bonus every 4-5 levels" sounds pretty reasonable to me.
The nearest thing there is to a "guide" might be to look at some published adventure modules for various levels and see what magic is given out there. Keep in mind, however, that the underlying expectation is that the PCs won't necessarily find all of it (this is another huge variable!); long-time experience tells me they find about 3/4 of it on average, but I've seen parties find everything possible in an adventure and I've also seen parties miss* nearly everything. But even only finding 3/4 would put the PCs well above the guidelines posted by others upthread: IME by about 7th level they're rolling in magic unless they've got unlucky with AoE saving throws causing their items to melt down.
Which is yet another huge variable: items in 1e can be destroyed. If you fail a save vs (usually AoE) damage such as a fireball or lightning bolt etc., everything you carry - including your magic - then also has to save or be destroyed.
Given all those massive variables, plus some other minor ones, the absence of any sort of guidelines is very understandable.

* - or unintentionally destroy it, which has also happened many a time.