Only saw one example at yesterday's Kempton Park Fair and that was incomplete had a cracked grip and was not feeding properly. This pistol was on Lawrie Armatruda's table and despite the attentions of the acknowledged expert, this particular 600 refused to function reliably. So, given the wide selection and variety of pistols on offer at Kempton, it would seem 600s are becoming harder to find.
Get one when ever you get the chance would be my advice.
The Plink-O-Matic is a nice BB firing variant of this pistol which is even harder to find these days.
Brian