Mr. Furprick;
Good evening to you.
I see that Higginson powders,
http://www.higginsonpowders.com/ says that they now have the Vihtavuori powders.
I note unfortunately that they only have 1lb containers and also that it is $39.50/per pound. The last time we ordered from them, we got very good service, but a bunch of us went together to defray the dangerous goods charge on the freight.
You can always call them for the details.
I have it on fairly good authority that there might be a chap at the upcoming Kamloops gun show that sells some of the Vihtavuori powders. I talked to him tonight and he doesn�t currently have 540 or 550, but is hoping to have some by the show.
Hopefully that is some use to you. Good luck, I know searches for specific parts can be a bear up here, but good luck anyway.
Regards,
Dwayne