I bought my vintage amplifier and speaker from Gopi +91 78928 58440. He is near Majestic/Dr.Rajkumar road.
George is in Whitefield
99027 77799. He has good vintage stuff but you need to have good bargaining power.
There are even some good dealers and even individuals over OLX. Standard rule is to use the chat feature, never share numbers until you have ample clarity and then share numbers, no advance to be given. Audition in person if purchasing something from the person and close the deal.