https://www.amazon.com/dp/B089SHBZL4/ref=cm_sw_r_cp_apa_glc_fabc_H1HJ42DY64CXEADWXRPA?_encoding=UTF8&psc=1

I used these for my warbuggies. I think they are 152mm long. They also sell bags of these at Hobby Lobby.

Just spray painted them black.