“The Omni Grey suit is the suit Omni officials are required to wear.”
The Omni Clothing terminals carry all but the male shirt for this set. That piece is available from the Secondhand Peddler in backyards.
If you don’t want to check the backyards for hours, two other items in-game have the same texture as the Omni Grey Suit Shirt. The Omni Special Issue Grey Jacket, available to Solitus as a reward from the Omni Tailor quests, and the Wet Anti-Radiation Body from the Fixer shop.
Chest: Omni Female Grey Suit Shirt / Omni Grey Suit Shirt
Legs: Omni Grey Suit Skirt / Omni Grey Suit Pants
Arms: Omni Grey Suit Sleeves
Feet: Omni Grey Suit Boots