Did some digging around & found some info on another forum which is a bit incomplete & mite have some mistakes also!
Karnataka old reg numbers.
MY - Mysore State
MYA - Bangalore, post MYB series
MYB - Bangalore from 1945
MYC - Chikmaglur
MYD - Commercial Vehicles
MYE - Bellary, around 1958
MYF - State Road Transport
MYG - Mangalore, post MYX series
MYH - Hassan
MYI - No information
MYJ - Bangalore
MYK - Kolar
MYL - Belgaum
MYM - Mysore
MYN - Mysore, post MYM series
MYO - Bangalore
MYP - Bangalore
MYQ - Bangalore
MYR - Raichur
MYS - Shimoga
MYT - Tumkur
MYU - Bangalore
MYV - Bangalore
MYW - Dharward
MYX - Mangalore
MYY - Bellary
MYZ - Coorg (Kodagu)
Post the MY series we have had the following numbers
ME Series - 1970's, MEA,MEB,MEC,MED,MEE etc
CA Series - Bangalore, CAA, CAB,CAC, CAD etc
CN Series - Largely away from Bangalore, CNZ(kodagu/Coorg),CNX
CT Series - Largely away from Bangalore, CTO,CTX
CK Series - Mainly Bangalore, CKA,CKD,CKL, CKM etc