How do I get Blacksmith Plans in Diablo 3?

I just learned from looking at the official Diablo 3 site that there are a variety of Blacksmith Plans that you have to require in order to craft certain rare and legendary items. I have not seen any of these drop so far in my game, nor have I seen them for purchase at the Blacksmith or other vendors.

Does anyone know how you get access to these plans?

Solution 1:

According to Blizzard, there are 3 Normal, 87 Rare, and 39 Legendary Blacksmith Plans. We know that the three normal ones are dropped by Izual in Act 4 on the respective difficulty levels.

Anecdotally by forum posts, it looks like people are finding one or two per difficulty (bnet forum post) from random monster/champion/boss drops, although one person notes none found on his way to Inferno. So far the only non-Blizzard list this gamer found was at d3db, and it just lists "Drop" as the source of each of the plans.

Solution 2:

Any rare mobs can drop the pattern. I have a friend whose highest character is a Wizard in Act 3 Hell and he has already managed to obtain 3 legendary item patterns, compared to me who has 1 in Inferno Act 3 and Inferno Act 1 and haven't seen 1 drop as yet. The plans are just random but as others have mentioned I have found several rare item patterns in Inferno but typically the basic armour upgrades - nothing outstanding. The only way to obtain the plans is by persisting with the game and killing as many rare/elites are you can. Most people say they get them in Inferno because they farm Inferno for those 1k+ dps weapons or elite items. I don't recall any high level player going back to Normal/NM/Hell to farm when they can quite sufficiently farm Inferno.