i understand that it drops off dungeons and pvps,
but at what rate can i expect it to function?
is it possible to get it Any time Before 80?
can i get it on fresh 80s? is it more common like a blue item, (farm-able?)
or is it like a purple item that i can only get a few and expect to use Very carefully?
It's pretty rare - I've never seen one drop from a dungeon though, not sure that's a thing - I believe they do have a chance of dropping from raid bosses though.
Battlegrounds I'd say are the most common, but not too common - On one of my chars I have 3 scrolls and I received 1 every 15ish bg wings.
I find that you usually get your first one quickly, I usually get 1 within the first 3 bg wins and then they become a lot rarer.
About 1-2 maybe even 3% drop chanse per WOTLK RAID BOSS for a scroll of deception.
I have done tons of raids with guildies and friends to transmog all my 10 characters, and we have all tried to calculate what the drop rate is, I probably farmed around 150 myself by this time and I get them all from Naxxramas / Ulduar and Icecrown raids, frankly, raids with the most bosses in it since every boss gives a % chanse to drop a scroll, the best for me by far has been Naxxramas due to how easy and fast the dungeon is, I get 1 scroll about every third Naxxramas I do. Raids with 1 boss in them are no good, even toc is not good for scroll farming.
My take on it is that the first scroll drops relatively easy from BG or raid bosses. I even gotten a scroll in dungeons with one char but rare. But I think that after you get the first scroll it is very hard to get a second. Usually if I haven't played one of my characters for a month or so I will almost instantly get a new scroll.
For active player who do both pve and pvp content you can expect 1 to drop every ~ week.
Droprate is about the same for the content.
Bg's take more time so it feels like the droprate is lower but if you think about it in a logical way there is no difference.