If you are simply after a convenient way to listen to their original tracks again you are in luck because since 2021 parts of The KLF’s catalogue have been made available in digital form through various streaming services.
However, if you are strictly after physical releases, note that all releases on the band’s KLF Communications label (UK) were deleted when they retired. While non-UK licensors of the music (including Arista and TVT in the US, Liberation in Australia, and Toshiba/EMI in Japan) will still have the right to produce KLF records for several years this will be for a finite amount of time.
Since it seems unlikely that Drummond and Cauty will ever release their products in physical form again, so you should think seriously about purchasing what you can now, while you can. Of course, original KLF Communications releases still crop up in second-hand record shops, and Facebook group members occasionally sell some things off. In the UK most of the foreign CD’s are available on import quite easily, while the original KLF Communications issues can be found in internet shops including eBay and Discogs.