I have 6 but no one i can find has alot.

Who would have most in the game.

I just went to the Gun Runners since for me they had 8000 caps. I waited a few in-game days and went back.

Depends, The gun runners always have 8k caps...

For a long time the store in Hidden Valley had 23k every time she restocked.. (that was awesome for making caps)

Right now Blake in the Crimson caravan restocked with 12.2k caps every time. (been this way for a very long time now so hopefully its permanent.)

If the blake thing isn't a patch fix then the gun runners are probably your best choice. Choose 3.7k? worth of ammo and then trade it for 8k caps and your gold bar..

What I do is just buy ammo, weapons, and armor that I want then reduce the price I pay with the gold bar.

Blake at Crimson Caravan is the seller to go to. Even after the newest patch on the PS3 version, he has 12,211 caps every 72 hours. If you don't mind waiting 18 days to sell all your gold you'll be alright. His stock doesn't seem to change if you spend 72 hours outside of Crimson Caravan. So you'll have to wait in front of him or inside the Crimson Caravan area.

I think I went to the 188, since it was probably the closest, and I was overencumbered LIKE HELL.

They had barely any caps at all, but it's not like there's much to buy in the game.

I managed to get 4 out and sold them all at the Gun Runners, basically buying weapon mods to make up the difference. Then I spent the money on implants at the hospital.

You could have taken them to the hologram vendors around the sierra madre before you left and traded them for old-world money. It is weightless and they have 2500 valued at 10+ caps each, it is what I do and just use it in place of caps when I'm buying stuff.