I found at least 2 places that stock them using a quick Google search.

Just the bullets
http://www.thegunsource.com/item/381...GR_50_BOX.aspx

New Old Stock Knight packaging
http://grizzlymike.com/blackpowder/K...FT_900205.HTML

If you want a similar bullet for MUCH less, www.wideners.com has the Nosler 45-260gr and 300gr Partitions for about half of MSRP.
http://www.wideners.com/itemdetail.cfm?item_id=528&dir=

I don't know about the Swifts but Noslers are a bit small OD than other .452s. They are actually closer to .451 like Barnes so you may need a different sabot than what shoots best with a typical .452 caliber bullet. In my bores, i had to use a MMP short sabot to get the same loading pressure as the Harvester short black i normally use with other 45s.