I use a number that I have collected over the years. Maxwell Sandford I think sent me most of them. The C41 I currently use was posted here, as Flexicolour clone, and works well. Its developer posted quite atreatise on his testing regime.
The RA-4 I use is from Maxwell's collection, and others, such as Ron Spier's old posts from the usenet days of perhaps a decade ago.
I saw an online posting of Maxwell's stuff discussed here a few weeks ago.
I have yet to find an as good as Kodak E-6 for all the steps for slides. Pre bleach, bleach, fix and stabilser I am happy about home brewing. The first developer home brew is almost the same. CD is a trick one, and I am still gathering notes on how to try to equal the commercial mix.
Kudos to Rowland Mowrey and Ian Grant for all of the knowledge they willingly share as questions on chem processes come up on this site.