A lot of people have fitted KYB KG5564 rear shocks to their Fiat 500s (Abarth, 500T, Pop, etc). These shocks are a decent upgrade over OEM and can be used as OEM replacements. They are not adjustable like the Koni Yellows which I still recommend over these. The KYBs also need extra hardware. A list is available of what you need below:
Note: Might be able to find them cheaper or available at other places.
1. 2 Shocks: https://www.amazon.ca/gp/product/B00.....