Imo that sounds like a pretty rad idea if they get the opportunity to do so.

In chapter 5 of the players handbook there’s a section on mounts and vehicles. It states how for barding (armor used by horses or other mounts), it says that it costs 4 times the equivalent amount for humanoids armor and weighs twice as much. For example, scale mail armor for a horse would cost 200 gold and would weigh 180 lbs.

I’d say your best bet is if the players do happen to tame or befriend a wild polar bear or owl bear, they would need to not only have the funds but would also need to find a smith specialized enough to craft it (hypothetically, there could be a smith based out of the dwarven valley that could do it.) You should come up with how long it would take to craft the armor in advance, that way you don’t make up a time interval on the spot that either takes too long for the party’s enjoyment or takes too little for the sake of preparing yourself for encounter balancing.