www.jetphotos.net/census/ is usually quite good for this sort of thing, if you haven't got it already. Doesn't seem to be being kept up to date, contrary to hopes when it took over Bill Harms' data from
www.bird.ch/bharms
But the 737 list sorted by registration -
http://www.jetphotos.net/census/list...reg&model=B737 - doesn't show anything with a prefix PA. And "PA-" doesn't seem to be a current ICAO registration prefix - see
http://www.airlinecodes.co.uk/regprefixcur.asp