A couple of things....
First: The Hodgdon Data Center lists up to date information for almost every commercially available cartridge--and even some that are not. The data is available for Hodgdon, Winchester and IMR powders.
Alliant does the same thing for their powders. The data is updated automatically to reflect changes in powder performance from time to time.
Written/printed data is invaluable as well, and I heartily recommend that any reloader accumulate a collection of data sources. As an example, I have (and consult) the Speer manuals from #10 upward; the current Nosler manual, Hornady reference manuals one and two and a few more.
But I find it very helpful to obtain a starting point--or actual load data--from an online source that I can pull up and cross reference in a matter of seconds.
Hiding in plain sight...