Hi Rich,
Unfortunately, to find the guy who makes inner and outer rockers for '41 Buicks, you're going to have to look in the mirror.

Seriously, there are no current repro parts like that for these cars. There are occasionally generic patch pieces on Ebay made decades ago that fit multiple cars and you can massage them to fit, but nothing new that is a direct fit part. The good news is that the rockers aren't all that complicated to make yourself if youre even a little bit handy. It's good practice with your welder, too! Check out my site below and see how a guy who's never done it before is doing it.
Hope this helps.