Next time your drivetrain is due for a total replacement, you could go with a SRAM GX 2x11 speed drivetrain. The cassette goes up to 42t. The crankset is 24/36.
You would lose a bit of top speed compared to the triple but your low end would be good enough for even the steepest hills.
This SRAM groupset is quite a few years old now and can be found for pretty cheap. It would be a lot easier than trying to piece together a custom cassette. If you use drop bars, there is a Microshift bar end shifter that works with this rear derailleur. You can use any random front bar end shifter since front shifting is friction. I got an old Shimano front shifter from my local bicycle recycler.
Last edited by Yan; 02-28-23 at 05:09 PM.