"Tomorrow let them see our strength, and weep whilst they their want of losing blame; their valiant folly strives too long to keep what might be render'd without shame."
- – "Solyman" (Common western misspelling of the name"Suleiman the Magnificent") Seige of Rhodes (opera, 1656) by William Davenant,
The Maccabian Janissaries are the masked, pious fighting force of the Holy shrine world of Maccabeus Quintus. Zealous in faith and fanatical in war, the Janissaries are the elite handpicked guardsmen of the planet who seek to spread the imperial words of truth to all corners of the galaxy. Because of this, many see that becoming a Janissary is the best form of pilgrimage; to be a pilgrim in a vast and unenlightened galaxy.
While relatively few in number compared to other regiments, the Janissaries more than make up for their numbers by being some of the most finely equipped warriors in the imperium with Flak armour Mk1-NonCardboard, badass silver masks to prove their faith to their blessed saint, Drusus and a disciplined Napoleonic shoulder-to-shoulder fighting style similar to the Mordian Iron Guard.
Their lasguns are shaped like bolters. Likely due to the Imperial faith's belief that bolters are particularly holy weapons. These guys are probably super effective against daemons and psychic enemies due to how faith works and that they're practically the Imperial Guard's Sisters of Battle.
Probably singing this https://www.youtube.com/watch?v=ZXZMIC-Z-XA, "The Janissaries March", while marching into battle.
Currently there are no miniatures supplied from Games Workshop or Forgeworld to justify their awesome, making them one of the most underrepresented if not lesser known regiments in the Imperium. To be fair, this probably has less to do with GW/FW being lazy and more to do with the fact that Fantasy Flight Games invented them, and "core" 40k probably won't ever go anywhere near it for licensing reasons. Luckily, their appearance is similar to a Power Armoured Space Marine or Sister of battle, take a few tons in metal off the top and add a few purity seals for good measure.
Victoria Miniatures sells greatcoat legs, so grab some Cadian arms and the greatcoat legs. Then use the pilot torsos from the Valkyrie/Vendetta kit. Failing that, just some good old Cadian torsos (sand down the chest if you're willing to put the effort in). For the head you can try to find a samurai head from somewhere and sand it down (or just leave it). To finish it off add some kind of backpack. A Scion backpack would be preferable.
GOOD NEWS EVERYONE! OUR REPTILIAN OVERLORDS HAVE COME TO THE RESCUE! They have just released Mask Helmets, which are pretty damn close to the Janissaries. Along with Anvil Industry bits and maybe some GW bits, should be able to convert your own force in no time.
You can also get Necromunda pattern lasguns at Shapeways which are pretty close to the art.
Sadly, the Reptilian overlords link is broken, meaning we ain't gonna get their masks for a while. We're sorry Janissary nibbas.
Unfortunately, it seems like Reptillian overlords either lumped their death mask heads into their new Patreon service (sending files so you could 3D print them at home which is a capability not many people have) or have just stopped selling them... Emperor damnit.
FORTUNATELY, FAITH IS ITS OWN REWARD