I am sure every infantry support weapon have a tracer round between a few rounds for it.
All full auto support weapons has every 5th round as a tracer round. Assault weapons or tactical weapons such as full auto/burst/semi auto rifles such as the AK47, Vz.58, AR15/M16 would not use tracer rounds.
Take into consideration that most weapons in the Fallout universe are civilian owned, and that tracer rounds aren't very common use for civilians.
Civilians might not use them but civilians can buy them. I have a stock pile of both soviet green tracer rounds as well as armor piercing Czech rounds including even a crate (880 rounds) of Armor piercing tracer incendiary rounds. So I think you should be able to obtain tracer rounds but they wont show you exactly where your bullets are going. Tracers tend to burn off their glowing element which ends up higher/lower/left/right/ahead/behind the projectile so its not accurate for use in a light weapon such as a BAR or an assault rifle. Works great in a medium to heavy machine gun though.
I don't think there was been a single WWII game that has been accurate in its depiction of weapons. Crap of Dookie is a frequent offender (I SHOT THAT GUY WITH A M1 GARAND 6 TIMES!!!)
Well its obvious you never played Red Orchestra Ost Front, that game is a WWII game that uses accutrate correct bullet trajectories where the bullets drop just like they do in real life over distance, they also have one shot kills, they have accuracy based off the real guns (the M38 carbine is less accurate than the M1891/90 or the M1891/90 sniper rifle), they even have bullet damage based off real ones. For instance a 7.62 caliber round would kill a person with a gut shot or a head shot but a smaller submachine gun pistol round wouldnt kill with a gut shot. This game is pretty much a real life war simulator where its not a buffed up one man army type game. You are crawling with tracers flying all around you bouncing up from the ground going all over the place. You get hit if its a flesh wound too bad theres no medics and no health kits to heal up.