here is this on ebay

https://www.ebay.com/itm/Kap-Pak-OK-Cub-039-049-074-099-Flexible-Needle-Valve-Model-Airplane-Engine/153684996580?hash=item23c856f1e4%3Ag%3ArkMAAOSwIM5dpR8Q&LH_BIN=1

Carl

If you contact OK Cub directly they might be able to supply the parts you need.
They have discontinued engine manufacture but still advertise service and some parts availability.
I bought a last edition commemorative engine and some parts a few years ago and the pricing and service was second to none.

Had no idea the OK business was still going.

Link: http://www.okengines.com/museum.shtml

Can not seem to contact them.                             Phil Bare

You might do better with the Kap-Pak type needle as shown in the ebay listing.  I would probably have more taper on it than the original.  Even the latest needle from OK was way too blunt, making them over-sensitive.  Some suggest that you need to file more taper on them, but I've found that it doesn't take too much extra taper to make the thimble bottom-out, not allowing the needle to fully close.

As has been said, I believe you can still get many parts directly out of OK Engines.  The needles they currently (or most recently) sell are different to the original in that they have a spring rather than a split thimble.  Depends if you want it to display as original or you need it to function better.

Rod.