Win 231 is the same as HP38. If you can't find one, the other should do. You should confirm this with Hodgdon. Older lots of powders may not be the same, but they have been the same for about a decade now, as far as I know. Finding WW231 is a chore these days. You just need to keep looking at all of the suppliers frequently. Some will allow a backorder, so you would eventually obtain some.
Was there a fire at some other facility, other than the one that produces Clays and all of it's variations? As far as I know, 231 and HP38 are still in production, along with most other Winchester, IMR, and Hodgdon powders, with the "Clays" line being the exception.
When you go to the trouble of finding a load that works for you, it's pretty hard to start all over again with another powder. I have over a dozen powders that would work in the .45, but might use only one because of accuracy, function, cleanliness, or consistency with one bullet or another. For plinking, it's one thing, for target shooting requiring accuracy, there is nothing like having the right components to duplicate the load that's been working for you. If you are looking for maximum velocity, there are a only a few choices that might get you there.
W231 is a great powder for the .45. I use quite a bit of it and have used HP38 interchangeably. Same powder, different name and brand. The only difference might be like you'd expect between lot numbers.
Keep looking, you'll eventually find W231 or HP38 somewhere. Hodgdon might also tip you off to who has received a shipment recently. It wouldn't hurt to ask. I found several powders at a local gun show a few months ago. Paid a little more than usual, but there was no shipping or hazmat.