For this achievement you need to find and equip three suppressors at the same time. 1 for your pistol and two for your main weapons which could be an AR, DMR, or SMG. This will obviously be very reliant on RNG and hoping you get good drops wherever you're looting. Also be sure to check the loot on players you killed as it's more common to take a suppressor from a fresh kill who might have had one.
After a 2019 update SMG / Pistol suppressors are now the same thing and compatible with each other. Meaning a pistol suppressor can be attached to an SMG and an SMG suppressor can be attached to a pistol.
The best two maps to go for this achievement would be Sanhok and Vikindi as they're both packed with loot.
EDIT: Thanks to AZT Sidewinder for confirming the VSS counts as a suppressed weapon.
EDIT: Thanks to Bricki for confirming the Crossbow counts as a suppressed weapon.