>Which do you own?
I own the Mk. XIX with the stainless finish in .44 magnum. Favorite gun, carry it daily.
>Where do you shop for ammo?
Sportsman's Warehouse. Nowhere else to do it really, other than my local mom-n-pop shop. They don't always have the rounds on THE LIST though.
Don't go for the gold unless you just want a decorative piece though. The only time the gold deagle was good was in Killing Floor, and even then that was just because it was amusingly tacky.
If you're low on funds, I'd just shop used. You can get them for $800, which is a steal compared to the $2750 I paid for a new one with mags. If you must go new and you really want the gold, save up and get it when you get a tax return or something. I wouldn't say a deagle is practical enough for the average person to justify paying that much for it.