HI Alex,
I would try a bearing supplier if you have a seal out and can measure it. I found replacements for my 352 box quite easily (simplybearings ? I can't remember for sure). It wasn't an exact match, I think the Renault on was 11mm wide and the replacement 10mm, but the inner & outer diameters were spot on and after all, that's what's doing the sealing. It was cheap, IIRC £5-6 each. I did fit them with sealant though, just in case....
Brian