Yes, ならん is colloquialism for ならぬ, which is a literary/older version of ならない. Practically, you should learn 我慢(が)ならない as a set phrase meaning "unbearable". We never say 我慢がなる. This ない is obviously a negation marker, but there are several fixed expressions where ない has been almost incorporated in a single adjective.

Other examples:

• 鼻持ちならない / 鼻持ちならぬ / 鼻持ちならん
• 聞き捨てならない / 聞き捨てならぬ / 聞き捨てならん
• やんごとない
• 不甲斐ない
• やむない

If you want to understand the なる part etymologically, this 成る【なる】 means something like "to accomplish/succeed" rather than "to become" (cf. 為せば成る). ならぬ/ならん by itself can mean "that's impossible" or "don't do it".

And also note that this 着た is not "who wore" but "wearing". See: Use of かける (N5 question)

Yes, ならん is colloquialism for ならぬ, which is a literary/older version of ならない. Practically, you should learn 我慢(が)ならない as a set phrase meaning "unbearable". We never say 我慢がなる. This ない is obviously a negation marker, but there are several fixed expressions where ない has been almost incorporated in a single adjective.

Other examples:

• 鼻持ちならない / 鼻持ちならぬ / 鼻持ちならん
• 聞き捨てならない / 聞き捨てならぬ / 聞き捨てならん
• やんごとない
• 不甲斐ない
• やむない

If you want to understand the なる part etymologically, this 成る【なる】 means something like "to do/accomplish" rather than "to become" (cf. 為せば成る). ならぬ/ならん by itself can mean "that's impossible" or "don't do it".

And also note that this 着た is not "who wore" but "wearing". See: Use of かける (N5 question)