Your best chance for a 1919 barrel is going to be another sporter, i.e. one with the barrel not bobbed.
That will be a long process as its date specific and if you want a real solid match, as near month specific as you can get.
They are out there but it takes a lot of looking
There simply are no surplus WWI barrels. As noted, they got shot out and then thrown away.
On the other hand, if the barrel simply needs to be cut and then crowned a gunsmith can do that. You won't have the barrel date, but you will keep the barrel and they tend to be accurate despite being shorter.