Source of mirror reflectivity data I am trying to find a source of mirror reflectivity versus wavelength for the typical protected overcoat Aluminum mirrors used in astronomy. I need this to cover the whole visible range (300-1200nm) and ideally machine-readable. I've only been able to find part coverage of the wavelength range or single spot measurements at a specific wavelength. 

The best I've managed is this page at Edmund Optics which has (small) plots but no table or downloadable file.
The spectral reflectance curve depends on the coatings applied.  For 'scopes used by people there is no point in maintaining reflectivity below 450 or above 700 nm.  You idea of &quot;visible&quot; range is, I fear somewhat optimistic.  You may be better off with an uncoated Al mirror (spectral curves easily found on the net) and giving up some signal in the photopic range.  -- or with a nice Ag overcoat, perhaps.
edit
Per request, some data on uncoated Al.
From   laserbeamproducts,

REFLECTIVITY OF PURE UNCOATED ALUMINIUM AT NORMAL INCIDENCE

Wavelength            % Reflectivity 
248nm                      92.6 
400nm                      92.0 
532nm                      91.6 
633nm                      90.7 
800nm                      86.8 
900nm                      89.0 
1um                          94.0 
3um                          98.0
10.6um                     98.7 
20um                        99.0 
100um                      99.4

An image published (by the author) at Researchgate