Reynolds made aluminium stems and bars from 1935 onwards - these were available anodised in colours as well as polished. AVA also offered aluminium bars and stems I think from c1937 onwards. Caminargent also offered aluminium stems pre-war. Aluminium components were made far earlier than many realise - Roman aluminium rims were made for Sunbeam and Rudge bikes from about 1907. These continued to be made into the 1920s. Chater-Lea offered a range of aluminium components in 1927/8 - hubs and cranks - they did not last long in the catalogue just a year or so - I think they must have been really quite unreliable. Constictor offered aluminium brakes by the mid 30s and Ambra Superga parts - brakes, pedals etc were offered at a similar time.
Hilary Stone, Bristol, England