@Miyuso - check out what @David Musgrave has done with halfling war-balloons (link), what @Mac Coxhead has done with Dark Age Irish head-swaps onto viking halflings (link), and what @Grumpy Gnome is doing with some creative kitbashing for gnomish halflings (link).
I think Persian and Afghan bits will probably mix pretty well with halflings, with a little creative modeling for some of the two-handed weapons - the key thing to bear in mind is that halfings have very short arms, so you'll probably want to trim off the halfling hands and human arms, and glue human hands onto halfling arms to make the weapons swaps work.
I like the way Mac's mix of Dark Age Irish bits and halflings works out, and I think the upcoming WA Dark Ages Goths set looks like it'll include some great bits for halflings as well: the head-swaps look much better than I expected! Grumpy Gnome suggested using the WA Persians as a source of odd gnomish hats, which sounds like a fantastic idea, and I think they'll work great on your project. The Persian bows and quivers can probably be adapted to work on the Halflings, with a little work.
The WA Afghan kits ought to mix in great with some Persianized Halflings - the turbans, swords and old-fashioned Afghan guns would make some very interesting Halfling soldiers, though adapting the guns to halflings might require some creative modeling - I've not tried it, but it would be an interesting project! The little Afghan shields are perfectly sized for halflings.
Northstar's Frostgrave Crewmen and Wizards I kits include some heads wearing turbans and some miscellaneous weaponry and spell-casting gear that might come in handy for your project as well.
A little made-in-the-USA miniatures one-man cottage factory called Eccentric Miniatures makes and sells some great little injection-molded medieval knight kits and bits in a smallish (25mm-28mm) scale; some of the figures look a bit small compared to standard heroic-scale fantasy miniatures, but the weapons sprues are full of small swords, hand-axes, shields, and maces that make for great weapons-swaps onto the halflings! The heads from the knights and archers kits look pretty good on Halfling bodies, too, and the archer accessories (daggers, hatchets, quivers, bucklers, napsacks, and maybe the longbows) will work great with Halflings as well. I think some of the maces and other bits might look good in a Persianized halfling army, and you might also want to check out the siege crossbows made by the same company - I think they might look brilliant in a Persianized halfling army (or any 28mm fantasy, Roman, Dark Ages, or Renaissance army for that matter!)
Mantic has recently released some hard plastic halfling sets that look like they might mix well with WA's halflings; most of these have boots, helmets, and breastplate armor, which might work well for more heavily armored halflings; I think the weapons and top-hats and other heads look like they'd look great on rank-and-file halfling militia.
Check out Reaper Bones plastic halfling miniatures, especially those sculpted by Bobby Jackson, for "hero" characters - these mostly have a traditional Tolkienesque look and feel to them, but it wouldn't be difficult to adapt most of them into rogues, leaders, and the like in a halfling army - they'll take head-swaps with Persians and Afghans pretty well, I think.
You might be able to get some use out of some 1/72 scale Napoleonic or American Civil War artillary, which would be small for 28mm human characters, but right at home with a Persianized halfling artillary team. Redbox makes a 1/72 16th-17th century Ottoman artillary set that should include some great guns, and the halfling-high figures might be a bit slender compared to halflings, but might include some great accessories to equip your halfling artillarists with.
Between the Persian influence and David's halfling war balloons, I'm starting to get a real Adventures of Baron Munchausen vibe off of this project! Sounds like it would be a blast!