Hi. Have a (patient!) trawl through a supplier's connectors, and cables, pages, and maybe check the datasheets available for current rating.
https://uk.rs-online.com/web/c/connectors/audio-video-connectors/jack-trs-connectors/
Not sure which part of the catalogue the other barrel jack connector would be in, but RS have a chat option where some-one can point you in the right direction for that.
I don't understand how a cable with nothing more than two connectors at either end can die in a few months, unless it's being "cooked", so in my ignorance I'd suggest seeing if you can get hold of a datasheet for the cable/connectors you have. Unlikely - but is the section (mm2) too small for the load, or are those connectors not rated for the actual load? It seems unlikely, but you never know.
If you buy the parts yourself, you will no doubt have to buy packs of 5 or 10 of each connector, hope they are simple to crimp/connect to the cable, and be forced to buy at least a few metres or 30 or whatever of cable no doubt, so it might only offset buying the $25 pack to see if the ones you make last any longer than a few months.
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Just thought, a probably/possibly more likely failure is something silly like a loose connection betweeen the cable and a connector from flexing them. If you have the time and inclination I'd try to take apart a "broken" cable, to see where the fault is coming from. The audio connectors are (hard work sometimes) slip on/off or screw twist on/off, the barrel jack one I don't know but will no doubt be a similar method, unless they have been glued, which shouldn't really be the case. In the worst of cases, just use a cutter/Stanley knife or similar (keep hands and fingers very behind cutting direction) to cut one open and trouble-shoot.
If it's coax cable, I doubt it's flimsy, but another point to consider, if the terminations on the broken cable are sound, is to try with a different type of cable which is more flexible, and if it has to be shielded there are quite a few "shielded pair" type cables available for power.