The codes 2051 and 9741 are BALM paint codes, which fell out of use many years ago. Even the old books aren't a great deal of use, because the colour swatches in them have gone dark over the years, and in any case the formulae they show are for the tinters used in nitrocellulose lacquer (lead-enamel). For what they're worth, here they are:
Skyline, 1958
Skyline, 1959
Fountain Blue
Ring Dulux-PPG customer service, tell them the name, the code and the year of the paint colour you're after, and they'll be able to find it and provide two-pack or acrylic alternatives. The year is important, because there were two different formula for Skyline Blue, a 1958 and a 1959 version.
PPG Australia
Customer Service & Technical Support
13 24 24
Toll Free Fax
1800 800 819
Hope that's helpful.