As far as I looked I never came across a polini cylinder kit, best chance you have is to look for a malossi 180cc cylinder kit.
You can find it on following link although they wrote 190cc it’s a 180cc
www.rrd-preparation.com/en/kit-high-engine-motorcycle-125cc-2-times/2232-20955-malossi-190cc-kit-for-125cc-honda-nsr-f-or-r-engine-crm-and-raiden-125cc-liquid-cooling.html#/2283-stage_1_engine_preparation-without
You can find it on following link although they wrote 190cc it’s a 180cc
www.rrd-preparation.com/en/kit-high-engine-motorcycle-125cc-2-times/2232-20955-malossi-190cc-kit-for-125cc-honda-nsr-f-or-r-engine-crm-and-raiden-125cc-liquid-cooling.html#/2283-stage_1_engine_preparation-without