I have been loading this bullet for a few years. I have found excellent loads with Reloader 7 and TAC. I know others who do well with H4985 and H335.
As you wrote in your post, there are a lot of powders that work well in the 30-30, and most of them work just fine with the 125 gr Sierra. Lyman's #48 says that Reloader 15 is potentially the most accurate with the Sierra 125 HP. If you have any of the medium fast powders on hand, it will probably work fine. If you have to buy a new powder, you might have a look at what is available in your area. Buying powder off the internet is easy but expensive if you only need a pound of powder. The Hazard Fee will be more than the powder. If you do buy on the internet, try to find the powder and primers at the same store and order them together, you will only pay one hazard fee that way.
Bob A