Hi RSAnowCA,
Hanno parts are difficult to find. However, Henry Nelson who has made all the replacement pistons/liners still has a few in his shop. Henry is 'semi' retired which means he doesn't want to take on any new projects, but still supports the many engines he has built and will provide finished piston and sleeve sets if he has them in stock (or, at least, the unfinished parts). I last spoke to Henry in April of this year and he had some finished and unfinished Hanno piston and sleeve sets. I have his contact information around somewhere if you need it.
The Hanno is a terrific engine, I've been running them since 1992 and have thousands of flights with them. Henry's piston/sleeve sets add tremendous longevity to the engine as you can easily get 1000+ flights with them.
Regards,
Will