Okay, so far i've killed these SMB's at these locations:

Capitol Building
GNR Radio Station
Evergreen Mills
And, this random ass lil train depot in the middle of god f'ing nowhere... I walked up to it and there was only 1 Super Mutant Brute there and I killed him, and then after I looted and left an SMB came outta nowhere to ATK me. Can't remember where I was...

How many are in the game?

And, where's the one(s) i'm missing located?

First, i think this is the wrong section to ask this question and second I believe there are 5 of them. There is one west to Jury street and Another one near a Talon Company Camp. You can check Fallouit 3 Wiki for details but you might find a lot of spoilers.

Nod. You're missing two of them. Ask in the FO3 Spoilers forum.

Eileen

You're missing the one in Takoma Park.

I found that one in Takoma and got the achievement. This can be closed. Thx to all whom helped!

how do u get to takoma park? plus visit my forum Fallout movie