Source for redwood log replacement

Hi,

I am new on the site and have a question.  I recently bought a redwood log home built in 1940 in California.  The home has some wood rot in a few areas.

The home has tongue and groove D-shaped logs on both the exterior and some interior rooms.  (The logs are essentially half logs attached to the wood frame of the building.)  I would call it log siding, but it is very think, the half logs are about 5.5" wide and about 2.5" deep.  So, I think half-logs describes it better.

Does anyone know where to get replacement logs?  Or do I have to have them custom milled?

Thanks,

Anna