When measuring conventional spokes, I take it you measure from the centre of the bend that goes through the hub as if measuring from the centre of the hole in the hub. Not adding anything for the bend. Or is the measurement required when purchasing an overall length as if you straightened it out. That sounds daft but not sure. Also can any one recommend some where to buy stainless or brass nipples and spokes. Cheers.

Spoke is measured from bend to end.
Any online retailer will sell spokes and nipples, your LBS will probably do the same.

Can only find spokes with aly nips.

lbs's have brass nipples for sale usually