Hi Steve,
To get you going in the direction you want first...and concrete supply distributor
should be able to source such a CMU....
I must share that I personally would never recommend to a client or student to use concrete in this fashion, or ever have it be in direct contact with wood...Especially logs for this type of vernacular building style. I like the concept, but would suggest stone, or clay brick, good solid gravel trench foundation, lime and/or cobb mortars, and a "rot resistant" sill timber species like cypress,
locust, catalpa, tamarack, hemlock or related species. I would also probably treat this sill with one of the "permi acceptable" modalities.
There is a great deal here on Permises.com covering this and related subjects to it...
Hope there was some value in this post...
Regards,
j