I think my 600 was serviced by City Air Weapons in Birmingham prior to me buying it so It may be worth giving them a call.
Alternatively, Dave Price - wonky donky on here may still service them for CAW.
https://www.airgunbbs.com/member.php?92340-wonky-donky
On gun price I bought mine for less than £300 but prices have risen since then, I think robs5230 recently sold one.
All the best Mick