Has anyone seen a reliable place to find 4e versions of OD&D, AD&D modules? anywhere? Palace of the Silver Princess specifically, but ANYTHING will do. Thanks!
No, but (contrary to some comments on the internet) doing your own conversions isn't difficult. You just need time.
(I converted a
bit of Dragon Mountain, for instance, mainly because some of the NPCs were interesting.)
2e didn't have a CR/monster level system, so you might find PCs confronted with monsters that, in 4e, are either really weak or really strong compared to them.
In 2e, often an adventure would have lots of low-level monsters and/or lower-level NPCs (eg bandits), which if directly converted means lots of "dice grinding" as you throw lots of d20s and hope someone rolls a 17+ and actually manages to hit a PC. Not fun for some groups, great for others. Tweak as your group likes.
Also, feel free to give "boring" NPCs powers. As an example, there's one encounter in Dragon Mountain (for 10th to 15th level PCs, so I assume 10th at start) involving Artur (a 10th-level fighter with a flaming greatsword), Arcana (a 9th-level wizard with a wand of fireballs) and numerous bandits, some of whom specialize in archery. So I would give Artur fighter or knight-like abilities (I gave him the Essentials knight defender aura/"counter"attack and Reaping Strike), Arcana got wand of accuracy and numerous AoE attacks, the melee bandits were leveled to about 6th (from their Monster Vault or MM1 version) and the bandit archers are hand-made artillery units of the same level.
Alas, my PCs are 5th-level, so they'll never see them anytime soon. I'll probably tweak them to match Dark Sun (make Arcana a defiler or something) and use them at some point.