Good luck! I recently went on a search for a P+350 for a friend, and I did find one (thanks Snork!), but it seems that people are holding them close. I will keep an eye out, but it may pay off to post a WTB ad here and on other venues.
Indeed, I can attest to the fact that they are not easy to come by. I wonder how many P+'s David has sold over the years. I'm guessing it's a lot, and people rarely sell them. I can't think of a better confirmation of quality than that.