The codes on the holders, strangely enough, are the codes for the holders.
In your search, you need phrase the query as 'insert for xxxxx tool'. The second letter of the holder code is generally the first letter of the insert code (but this is not true for the STDCR).
Five of the seven tools use standard inserts (of three different types – Cxxx, Sxxx and Wxxx). The threading and parting tools use a non-ISO insert but these are both currently shown as available from Warco.
I do not think you will not find this toolset among the Premier League ME suppliers, but if you have a scout around the other divisions (e.g. Chronos, RDG, Axminster, Chester, Armadeal) you might find that some of them are more forthcoming with info. than others.
Please see also this thread:
https://www.model-engineer.co.uk/forums/postings.asp?th=170078
but the RDG item mentioned therein seems to have disappeared from their site.