Tubular stem raisers work, steel tube rolled down at the bottom,
so its OD fits in the fork, a wedge bolt tightens it in there.
and the top has an ID to accept your existing quill stem in the upper section.

IE double diameters, on the tube ... Outside on the bottom = inside on the top.

in 22.2mm, aka 7/8" and .833" and 9/8" type.

Most distributors have them in their stocklist.

they are shown as #SM248, towards the bottom of this page: http://sheldonbrown.com/harris/stems/index.html

available, I expect on request, from UK shops.