I heard some rumours that Barnes have stopped making 450gr and 600gr original in .510". Can anybody confirm this?

Thomas:

http://www.barnesbullets.com

Click on the "products" box at the top of the page, then select "Original" for the listing.

It seems they are still offering the .510/450gr flat nose soft point for lever action use. Most of the old heavy Originals are gone the way of the dodo.