MY initial thought would be to call Shilen, in Ennis, Tx. They're due north of you on I-45, so if you have reason to visit the D/FW MetroMESS, they're on the way. The turn-around COULD be shorter from out-of-state suppliers, but you'd certainly lose the logistical convenience.
Point of curiosity: The original .220 Swift barrels had a gradual twist compared to other cartridges, to optimize for the lighter projectiles. Are you contemplating a faster twist, to stabilize heavier bullets?
How bout that. I had no idea Shilen was based in Ennis. I go up to dfw often. Though I'd probably just order something unless it really needs to be stupid custom.
No. I want to stay true to the lighter faster barrel-burning rounds. 40-50gr
I might be tempted to optimize for something slightly heavier, though not WAY heavier. I can understand the wish to keep it as it came to you, though. I have 87 .220 Swift cases, in unknown condition. If you'd like them, they could be had for somewhat less than what I'm seeing them priced at the usual places.
Putting load data through the noggin, I might be persuaded to load some 55gr Vmax's in it. But I still think those fall into the standard twist rate for the rifle.
There's another consideration about using the heavier projectiles. Barrel life is a function of the inverse square of the average velocity of the projectiles run through it. If you shoot all your ammo at 4000 f/s and the barrel lasts, let's say, 1000 rounds, if you were to run the same projectiles through the barrel at 2000 f/s, the barrel would last for about 4000 rounds. If you use heavier projectiles that have a muzzle velocity of 3600 f/s, the barrel would last for about 23% more rounds.
I have NO idea of what the actual barrel life for a .220 Swift is. I just used the numbers above to illustrate what I'm saying.