I got all of my chunks of Cloudstone by farming the Flying Mantas at 4-3. All Mantas have the potential to drop items in inaccessible areas, but the ones at 4-3 are a little more controllable. I only take out the ones in the other areas where they are problems for me. But I usually can't get what they drop.
This assumes you have beaten the Storm King archdemon already. If you haven't, I have found it best to use Warding and run like heck to where the Storm Ruler sword is, get that and run back to the entrance of the area to be prepared to get rid of Storm King. If you don't have high enough stats to pick it up, you may need to equip the Ring of Herculean Strength. So you might want it and do want to have the Thief's Ring equipped.
In 4-3 for farming, go from the Old Hero archstone-some go directly into it from the Storm King archstone, but I've done that and gotten ganged up by the mantas really quickly and killed so to be safe I go from the Old Hero one. I take Storm Ruler, Thief's Ring, usually the Ring of Avarice. My female character has the silver bracelets. The ring of Avarice and bracelets are for more souls.
You have to decide what other equipment works for you. I at one time used the Adjudicator Shield for some HP regeneration but changed to the Purple Flame Shield for more protection. I also take along the Warding Spell, some Spices, high power grasses.
There are also 2 crystal geckos here that give out Darkmoonstone, so you might want to be prepared for them too.
