Howdy
I don't have a Double Action 44 Frontier Model (44-40) but I have a couple of the 44 Russian versions. The only real difference between the 44-40 version and the 44 Russian version is the 44-40 version had a cylinder 1 9/16" long vs the usual 1 7/16" 44 Russian cylinder. Some of the later 44 Russians also had the 1 9/16" cylinders. The frame window on the 44-40 versions were stretched 1/8" for the longer cylinders.
The mechanisms should be the same, including the main springs.
Check out Numrich Gun Parts. They have a few parts for the Double Action 44. They don't have any hammer springs right now, I just checked. But there stock varies as they buy old guns and part them out.
Sorry, you can't have either of my springs, but the spring from either model should fit.
Check out Numrich Gun Parts. They have some parts for the 44 Double Action now, but no mainsprings. Check them over time, their stock varies as they buy old guns and part them out.