Hertford Choral Society has a number of sets of music in its library that are available for hire. The list is kept on the gerontius.net website which also offers a wealth of information about choirs.
To find your way to the Hertford Choral hire library (and to be able to request music for hire), click on the following link to the gerontius hire section : http://www.gerontius.net/findscores.shtml
When you get there, look for the 'Owned by' box, click on the downward arrow in that box and a list of all the choirs who have music for hire will appear. Highlight 'Hertford Choral Society' then press 'Find scores' (you may have to scroll down to find it) and wait for the list to appear!