I have a couple .30-06 style actions for M-70 where the magazine springs don't seem to have the power to push the cartridges up so that the bolt can engage them for feeding the next shot.

Are there stronger springs for this task...Does Brownell have something?

I've had this problem with a Ruger 77 in 7MM Mag as well

Brownell's carry what they call a 10% heavier spring for the Mauser. This would be your best choice.
I used to use the old P17 springs untill they dried up.
Then went to the old Weatherby 378 spring. However weatherby changed the spring in the early 90's.
I make a copy of the old 378 spring but use it only in drop box guards. As it is really to heavy for most standard depth boxes.
Jim Wisner