www.wideners.com is a source for components. I believe that they also carry the Hornady .50 BMG press/die package. The Hornady is said to be back ordered.
www.statearms.com offers a RCBS press and C&H die package.
For more info, check out this board www.biggerhammer.net/barrett/wwwboard/
Surplus military powder is available here in the States for $3-$4 a pound, but I do not believe you could get it imported from here.
However, definately take a shot closer than 1000yds. A shot at 600yds with a STURDY rest is about as far as I would want to go.
Shooting at 1000yds is NOT like setting a 100yd zero and then thinking that 25MOA elevation (100 clicks at 1/4" a click) is always a 1000yd zero. Depending on wind, air temp, humidity, barrometric pressure, altitude, slant angle, ect that 1000yd 'zero' WILL easily change as much as 6 feet or more. Also, only the best guns are 1MOA or less firearms. These guns CAN shoot sub-MOA at these distances, however most guns (Serbu, LAR Grizzly, AR-50, AR Upper, Maadi, Barrett, State Arms, AMAC) are 1MOA or larger (up to 6MOA on trade-in Barrett 82A1's). Also, this is with a proper rest to shoot from. Feild work will open this up to 2MOA or more for the best .50's.
Then we get into ammunition. Most of these 1000yd guns shoot match bullets that are a solid piece of bronse, steel, copper, ect that are machined on a CNC machine to exact tolerences. They make GREAT target bullets, but crappy hunting bullets.
My recomendation to you is this:
1) Get the RCBS BMG Reloading kit ($350) IF you are going to reload. Reloading for the .50 is expensive, but not as expensive as getting started. If you're going to shoot a LOT or enter into the 1000yd FCSA matches, then reload. If you're going to shoot less than 200 - 300rds a year, buy loaded ammo (Ammoman, Watsons Weapons, HSM, ect) for $1.25 - $2.50 each.
2) Get the book 'The Complete .50-Caliber Sniper Course, Hard Target Interdiction' by Dean Michaelis. This is a fount of knowlege.
3) Go to http://www.biggerhammer.net/barrett/wwwboard/ & http://www.fcsa.org/visitors/index.html?contents.html&title.html&visitors_vendors.html These two resources are the best on the web. Also, READ as much as you can before asking a question. Either the answer will reveal itself, and/or your questions will be more precise.
4) For a long range hunting round, the Hornady A-Max (750gr, aluminum tip, lead core) is your best bet. Many companies load these in their rounds (aaa-ammo, HSM, Arizona Ammunition, ect) and it works great, but it's also $4 - $5 per match round. IF you do get into reloading, this combo is hard to beat: 750gr A-Max bullet, H50BMG powder, CCI#35 primer, in any boxer primed brass (brass of all the same year & manufacturer = greater accuracy). Start at 205gr and work up in 5gr incriments while checking for signs of pressure. Find what powder charge is the most accurate in your gun and enjoy.
The 50 BMG is NOT cheap to own/operate. It WILL be expensive, but a lot of fun (I have two of them).