It is probably not a strength issue.
Arm endurance training is challenging for most people due to the lack of equipment. First choice: Get out often skiing, both touring and XC classic skiing will help this. Next: Concept 2 Skierg. Next: An old Nordic Track. Often found at garage sales at give away prices. I have even bought just the poling/arm trainer from a NT off eBay for something less than $20 and mounted it on a wall for poling simulation. Next summer and especially fall take you poles on your mountain runs and use your arms too to get you up the hills.
No plans for a ski mountaineering pod cast but the principles of training for all these uphill sports are similar that hopefully you got some useful info from that one.