In some cases there’s a perfect overlap (e.g., between Orkney and Shetland and the Insular Scots dialect), but in many cases I’ve had to split a council area in half, so the numbers won’t be very precise.
Bearing those caveats in mind, the numbers I came up with are as follows: West Central 551,984; South East Central 277,836; Mid Northern 230,380; North East Central 221,027; South Northern 101,913; South West Central 75,501; Southern 34,873; North Northern 24,226; Insular 19,266.
It’s interesting that the Central dialects (roughly the ones spoken in the Central Belt) account for nearly three quarters of all Scots speakers.