Draw out the difference in diameters with a compas on a piece of paper, it's not much difference and well within what you can do with a file or grinder to a scribe line, quite accurately. No milling machine necessary.
The perches wrap around the tube well less than 1/2 way. Even at half way around your 1/8" difference in diameter is 1/16" on either side front and back. No need to take any material off the center of spring perch, so adjust radius tapering from less than 1/16" front and back to nothing at the center. You can cut out a piece of card stock same as axle tube diameter or setup compas and scribe or trace or swing the desired radius on store bought perches. Lay it out so same amount is removed front and back of the arches and alignment is nothing to worry about.
I think you'll find that easier than making perches from scratch yourself, and cheaper than having something special made to your drawing.
Trust in your ability or ability to learn and give it a try.
