Like the others mentioned, Grady Whitlock is still raising horses. He has several farms, one of his primary farms is in Beckley West Virginia. The 4 Gs stood for 4 Generations of raising horses as Grady's Father, and Grandfather both raised horses/ponies and now his sons are involved to some degree.
Many years ago he was an AMHA Director. He elected to begin his own registry several years ago called the Gold Seal registry. He still has a few AMHR and AMHA breeding stock, although they are rapidly decreasing in numbers.
Back in the Miniature Peak, Grady had a couple of sales which were quite impressive (held in the ball room of a hotel), and you will find the 4 GS prefix in many larger farms' breeding programs - He spent some significant dollars purchasing some top quality breeding stock - Sons of Egyptian King for example.
Today, his sales are more like grade little horse sales - It is important to note that if the horses he runs through his sales only have Gold Seal papers, it is not possible to register them with AMHR, although if under 34, hardshipping with AMHA is an option, and then you could register them with AMHR.
I hope this helps.