If you take on this question, please only respond if can confirm that
the poster is available for sale: I am looking for a large poster /
reproduction  of a painting by Elizabeth Louise Vigee Le Brun -
1755-1842.  She painted a portrait of Princess Pelagia Saphieha, nee
Potocka - it is also spelled Princess Sophia.

Here is a sample of the painting:
http://www.batguano.com/sapienna.jpg

shimmy,

I believe that the name "Sapieha" is a surname for both Princes and
Princesses, rather than a feminine first name "Sophia".
http://pages.prodigy.net/ptheroff/gotha/sapieha.html

"Potocka, Pelagia Roza comtesse 
Birth : 31 AUG 1775 
Death : 12 MAR 1846 Paris
Gender: Female
Parents:
  Father: Potocki, Stanislaw Feliks Szczesny comte
  Mother: Mniszchówna, Józefa Amalia comtesse
Family:
  Marriage: 1793 in Grodnie 
Spouse:
  Sapieha, Franciszek prince
  Birth : 28 FEB 1772 Varsovie
  Death : 30 MAY 1829 Dereczyn
  Gender: Male
  Parents:
    Father: Sapieha, Aleksander Michal 
    Mother: Lubomirska, Magdalena Agnieszka princesse
Children:
  Sapiezanski-Siwierski, Eustachy Gatan prince
  Sapiezanka-Siwierska, Aniela Angelica princesse"
http://users.skynet.be/nobily/nobily/dat14.html

This painting is in the traveling exhibit "Leonardo Da Vinci and the
Splendor of Poland: A History of Collecting and Patronage" currently
at the Museum of Fine Arts in Houston, TX, through February 16, 2003.
http://www.mfah.org/main.asp?target=exhibition&par1=1&par2=1&par3=98&bhcp=1

The exhibit will then be shown at the Fine Arts Museums of San
Francisco / California Palace of the Legion of Honor from March 8
through May 15, 2003.
http://www.thinker.org/press/press.asp?presskey=110

While I was not able to find a poster of this painting, I believe that
a print of it exists in the exhibition catalogue, the pages of which
are 9.74" x 12.26":
http://www.polonia.com/polishbooks/product.asp?sku=2122
http://www.amazon.com/exec/obidos/ASIN/0300097409/ref=ase_photcitalfineart/002-4903071-9179231

According to the Bat Guano website, this painting is owned by the
Royal Castle in Warsaw ( http://www.zamek-krolewski.art.pl ), and
Andrzej Rottermund, Director of the Royal Castle, was a contributor to
the exhibition catalogue. You may want to consider contacting him to
see if he can tell you whether a print is available:
The Royal Castle
Plac Zamkowy 4
00-277 Warsaw
tel. (048 22) 65 72 170
fax  (048 22) 635 72 60,
     (048 22) 635 04 98
e-mail: zamek@zamek-krolewski.art.pl
http://www.zamek-krolewski.art.pl/kierowni1.htm

I hope that you are able to find exactly what you need!

Regards,

aceresearcher

aceresearcher,
Thank you for your comment.  Although I have followed up on your
links, I have not been able to find a high(er)-resolution of the Le
Brun painting.

However, that does not negate your research in any way, which was
comprehensive and thorough.  In the future, I will keep you in mind
for other questions that I may have.

Thank you for your time.