2000 and 5000 IU are quite common and can be bought at any US pharmacy and many grocery stores. It looks like 10000 to 50000 IU pills are easily available online: http://www.amazon.com/s/?url=index%3Dblended&keywords=vi...

For what it's worth, I supplement using the 5000 IU pills taken at about 7/week (irregularly, making up doses as necessary). I recently had my blood tested for D3 levels, and found it was close to but not exceeding the standard recommended level.