I would like to get a copy of a Baltimore Catechism that was in use in
Catholic schools in the 1950's.  Does anyone know where I could find
one of these books?

Hello.

There were various editions of these books for different grade levels
(No. 1, No. 2, No. 3, etc.).

Here's an eBay listing for the sort of book that you want:
"Baltimore Catechism Bk/1952"
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3536388831&category=12571

Abooksearch.com, Abebooks.com and Alibris.com list many catechism
books of the same vintage:

The New Confraternity Edition Revised Baltimore Catechism and Mass #3.
1952 •
https://secure.abooksearch.com/cgi-bin/bookfinder_order.cgi?booknumber=2864392

Baltimore Catechism No. 1 (1960 edition)
https://secure.abooksearch.com/cgi-bin/bookfinder_order.cgi?booknumber=3490686

THE NEW CONFRATERNITY EDITION REVISED BALTIMORE CATECHISM NO. 3, 1954
http://dogbert.abebooks.com/abe/BookDetails?bi=196086986

The New Confraternity Edition Revised Baltimore Catechism and Mass #3
(1952)
http://www.alibris.com/search/detail.cfm?BID=8067357081

1949 edition available from Abebooks:
BALTIMORE CATECHISM NO. 2
http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=207923572

1949 edition available from Abebooks
BALTIMORE CATECHISM Catechism of Christian Doctrine, A
http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=187857420

1958 edition available from Abebooks
CATECHISM OF CHRISTIAN DOCTRINE
http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=97431151

1960 edition available from Alibris
A Catechism of Christian Doctrine
by Third Plenary Council Of Baltimore.
http://www.alibris.com/search/detail.cfm?BID=8143266576

PCPbooks.com lists several books such as:

# Catechism of Christian Doctrine, A: No. 1: Prepared & Enjoined by
Order of the Third Plenary Council of Baltimore
 Baltimore, Third Plenary Council of / Ellamay Horan, study lessons by
 1936 168p pb Bi(F)Pg(G) $14.00  #3089
http://www.pcpbooks.com/booklist/booklist0021.html


If you're just interested in the content, many web pages feature
transcriptions from these books.
Example:
The Baltimore Catechism
http://www.catholic.net/RCC/Catechism/Doit.html

search strategy:
"baltimore catechism"
catechism, doctrine, baltimore
alibris, bookfinder, abebooks

I hope this helps.

Thanks for the very thorough and prompt response!

Thank you for the tip.
-juggler