You may still be able to get some of these from Morgan with the p/n Richard gave but they were in short supply recently. Not so sure that there is an alternative poly bush though, unless anyone else knows otherwise?
Phil Bleazey did get some made but his stock has gone to Avus Auto AG in Switzerland,
www.avus-auto.ch, they may have some? I believe that mog3wheeler.com in Sheffield UK are also looking at getting another batch made. You could always try M3W Services as well.