Interesting - I'm not massively familiar with the organisation, but I recognise some names and have had a quick glance at at some source collections. Sadly, I'm missing most of my books on the Communist Party of Great Britain (CPGB) during the Second World War, which may well have some more context on the organisation, but I'll do what I can to give some information.

The Joint Committee was founded on 7 November 1942, the anniversary of the foundation of the USSR, and was active until 1947, when the balance of funds remaining (£15,000, quite a sum actually) was signed over to the Soviet Embassy. In terms of composition, it is very much being run by quite prominent individuals, albeit those with progressive sympathies, and had ties to the Soviet Government, with the Soviet Ambassador (Ivan Maisky) a key patron of the organisation. One of the organisers I remember well is the Treasurer, Sir Peter Chalmers Mitchell, who was a prominent zoologist who had run in the Scottish Universities parliamentary by-election as an independent progressive candidate, although he came dead last. My suspicion is that there is a great deal of continuity between this organisation and some of the more genteel Aid Spain organisations set up to provide humanitarian support for the Spanish Republic during the Spanish Civil War - I seem to recall the Dean of Canterbury popping up in that context too. It's worth noting though that this does not appear to be a CPGB initiative, although they doubtless approved - overt communist involvement would have likely scared off some of the donors this committee hoped to attract.

That said, the Communist Party did correspond with, promote and run ads for the Joint Committee in their newspaper, the Daily Worker, which is where I've gleaned much of this information. The Trades Union Congress and People's History Museum archives also both have several hits for the organisation, including published annual reports, correspondence, pamphlets and the like. One key project that keeps popping up was financing a hospital in Stalingrad in 1943-4. I found one list of donors in the Daily Worker from January 1944 which made for curious reading - £5,000 from the Mineworkers' Federation of Great Britain alongside £1,500 from a collection of international diamond firms (including De Beers) and £600 from 'the Proprietors and Patrons of the Spotted Dog, Willesden". Although there's a preponderance of trade unions in the list, the appeal clearly had a wide audience, reflecting broad enthusiasm for the Soviet cause at the time.

I hope this is helpful - if you're looking for local organisations that might be interested in collecting it, it may be worth contacting the Glasgow People's Palace Museum.