as title says. anyone help me out?

Gunrunners sometimes have it, try Mick & Ralphs

ok thanks for the reply. ill try mick and ralphs, my gun runners hasnt updated their inventory yet.

Mick & Ralph's is your best bet early on if you get access to their special inventory. It's mighty expensive though.

More location:
Dino shop at Novac often sales c4 and detonator
Good Spring General store often sales detonator

There's a tonne of C4 in the Camp Guardian caves, out to the East of Camp Golf and Bitter Springs.

Crimson Caravan
You can also find a few other free stashes at Black Mt. and if a high enough lockpick skill there's a briefcase in the cocktail lounge in the Lucky 38.

Vault 34 armory has a detanator, and around 3 C4. It's not the best, but it's the only place I have found c4 in my 35 hours playing....

There's a disclaimer on that stash...

I found my detonator for sale from the woman who runs in the bar in the mojave outpost along with 3 c4. Found another c4 for sale from either the guy who runs the gift shop in Novac or the random unnamed merchant who is sometimes found right in front of you when you fast travel to Novac, I can't remember. I got my last c4 off the corpse of a guy you run into at the very first stage of the quest the van graffs at the silver rush give you.

later game traveling merchants usually pack around 3 of them + detonator.


Also, why is it that the C4 "plastic explosive" looks so much like a bottlecap mine? and why does C4 roll downhill.. isn't it supposed to stick to the surface? they screwed up again.. trying to implement something new and failing miserably.. -.-'

plastic explosives can be formed onto objects but it won't just stick to something in brick form, you have to mold it and apply some pressure for it to stay put.