I would contact Sharpe. They do make a "legacy" cup and lid assy that would fit your gun PN 6690. That's what they will probably refer you to as that gun is old (SGF98 I'm assuming) and those cap assy's have probably been discontinued for many years. Maybe just the lid assy for the replacement cup will work with your cup. I couldn't find the lid alone searching so that is not a good sign though. Contact Sharpe though and they may be able to help. I wouldn't get too hopeful though.