Wanted: Oil Filler Cap for TR3A

After 20 years of slumber, the 3A that I purchased 1.5 years ago is almost ready to return to the road.  Very exciting.  Unfortunately the shop that rebuilt my engine lost therocker cover oil filler cap and I'm trying to locate another.  The cap that was lost was painted black and did not have the "dimples" but anything that fits would be welcome.  The car is currently a mechanically refurbished but scruffy driver, so no big deal if the piece isn't well finished.
 
Thanks in advance.....Albert