Expensive for decent sealed ones.....https://simplybearings.co.uk/shop/p43730/4TCR0643L/0643-NTN-Narrow-Section-Steering-Head-Set-Taper-Roller-Bearing-30x52x16mm-SEALED-MODEL/product_info.html
https://simplybearings.co.uk/shop/p43727/265215-Narrow-Section-Steering-Head-Set-Taper-Roller-Bearing-26x52x15mm/product_info.html
15mm for the top one.....