I have found the needle brearing size to be 18 bore 24 od
Sourced from http://simplybearings.co.uk/shop/p555328/HK18162RS+Budget+Drawn+Cup+Type+Needle+Roller+Bearing+Open+End+Type+18x24x16mm/product_info.html
These include seals at £3.49 each.
I am making my own pins from 18mm Silver steel.