239 polariser can be found on this link - 239 Polariser - LEE Filters

It is available in a width of 48cm (19") 
They are available in the length you require, in 30cm (12") increments.
Smallest size is therefore 43 x 30cm, but you could order 43 x 60, 43 x 90, 43 x 120 etc.

You can purchase any LEE Filters Products through a dealer. You can find the list of our dealers here: Dealer Locator Global - Find Your Nearest LEE Filters Dealer

If you are in the UK  then this can be purchased directly on LEE Direct;

UK - LEE Direct | Masters Of Light | LEE Filters (leefiltersdirect.com)

LEE FILTERS