Maccabian Janissaries
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 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.
Modelling
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.
or better yet Victoria Miniatures sells greatcoat legs, so grab some cadian arms and the greatcoat legs, then if you can find em, use the pilot torsos from the Valkyrie/vendetta kit or failing that just some good old cadian chests (sand down the chest if your willing to put the effort in) then my suggestion for the head would be to find a samurai head from somewhere and sand it down (or just leave it). then add some kind of backpack (a scion pack would be preferable but you could get away with any other guard pack).