Have you tried Wisner's (360-748-4590 | Fax 360-748-6028)?
I am not sure how well a liner will work on that barrel. The .32 ACP is a fairly high pressure round (c. 20k) and that would be on the high edge of the pressure range usually recommended for a liner. I am also not sure about the rifling twist, but I guess that would not be too important on a pocket pistol.
In the past, Numrich has had new manufacture barrels for all variants of the 1903 Pocket Hammerless. Their web site does not currently list them (why didn't I buy two when I had the chance?) but says to call 866-NUMRICH (866-686-7424) if an item is not found. May be worth a try...
I have never done it, but that barrel should not be too hard to make given a piece of .311" groove diameter (.303 cal.) barrel and a lathe. Probably not cheap, though, unless a DIY job.