never did find the regulator but...
my water pressure problem sorted itself out. In thinking about it, I had moved from Mexico (no water pressure) to The Shady Dell (lots of water pressure) to this here spot and I think that pressure valve got confused. So I used the holding tank and pump for a few weeks...once in a while I would switch to city water and the pressure would build..then I'd go back to the tank until finally the pressure is now about up to normal.
Anyway, I thought I'd post an update. My trailer never ceases to amaze me.
BTW, the other night, the electricity went out in my neighborhood. I was the only person with lights and a running fridge. Airstream life is grand.