I've looked everywhere. San fran, Redding, Klamath, that town near the ghost farm, everywhere. But nobody has more than like 500 gold. And when they do, they don't have any good ammo or guns to buy. Where can I find some good traders? Need some ammo for my new scoped SMG I found, and I want a good side arm like a desert eagle, as well as some shotgun shells. So where are some good traders, with plenty of cash or good items for sell? Thanks.

None of the traders carry a large amount of money. Its intentional.
Just buy expensive things off them with caps, then get your caps back by selling them lots of cheap things.

For good shops, go to San Fran, NCR and New Reno. Vault City is quite good too.
There's a guy in Redding with a lot of caps~ In the Casino

I'd say San Fran has the best trader for weapons, such as Gauss Pistols and Rifles. You may have to come back several times before you'll find what you want. Don't forget to search both tables, as for caps.. like Calgone said sell cheap things to them for their caps.

The Casino at redding's cashier usually carries a few thousand.