gas filler cap plug

[Andrew Packard <apackard68@comcast.net>]

Hello list
This is for those of you familar with the TR250 magnetic "Racing style" gas 
cap.  Originally it came with a rubber plug that was attached to the gas cap 
(lid?) and had about an inch or so of rubber protrude down into the gas tank 
neck to seal it.  I've only seen one TR250 with this plug still in place.  
Anyone know if this is a part that is available anywhere?  
Andy
CD6521L