Just an update here.
I've learnt a lot since posting on this subject before.
In Australia and New Zealand we use the paint brand called "Dulon".
Dulon tinters have their own codes so despite Dulon paint being connected with PPG paints and ICI, the ICI formula provided by Brett in Post #5 meant nothing to them.
At the moment, Toyota "Sky Blue 854" in Dulon is mixed from the following formula:
Volume 500 ml
Tinter Cumulative Wgt (g)
Further info about this paint (as listed on my paint supplier's computer - Yes Apparently 854 WAS still on it):
Name: BLUE (Australia)
Vehicle Part: Body
Period used: 74-81
Finish Effect: Solid
Colour Reference: AVA6 (17349)
Mixing Scheme: 526 Dulon DGS
Match Category: Good match
Recipe Date: 03-Jul-1981 (Current)
Layer: Main Layer (AVA6)
Lead content: 0.0%
VOC: 0.32 kg
PS. This info is probably useful only to people in Australia or NZ where the Dulon brand is sold. (I don't think it is sold anywhere else.)
Also, a good paint supplier (and I don't mean simply a spraypainter's shop) will be able to do a perfect paint match for you if you provide a sample from the vehicle (such as the fuel filler cover bearing the original paint) without the need of providing them with the paint formula.
But I like to give them the formula so they can get the match "near perfect" straight away - and then, the way I see it, "perfecting the match" should take them less time/effort.
I fear as time goes on, the formula for my truck will be removed from my paint supplier's computer (because the management hierarchy are always adding and removing formulae).