I had a similar problem when trying to find a match for my wheel colour which was a bright silver, I had only minor marks on the rim and wanted to repair and blend rather than paint the whole wheel.
I ended up taking the wheel into Halfords and me and the sales assistant laid all the bright silver metallic car silvers on the wheel and independently selected our best colour match.
For me it was a fiat colour, but this may not be best for your original BMW silver as I had my wheels refurbished some 5 years earlier.
I think Halfords also offer a colour match spray option but more costly so I thought I would give the Fiat silver a go. Turned out really well.
Hope the above helps
