Hi Dieselman,
My seal problem was with smaller pumps of similar design on later aircooled Listers, so can not quote you any useful part numbers, but I found a helpful guy on the service desk of one of our major injection service shops here in West Australia. He said the seals were not normally sold seperately, but he understood my problem, and went to their service shop and got them, and mailed them out, for something like a dollar each! Quote the pump model and explain your problem, and you might just be that lucky.You can only try.
If you have trouble removing the damaged seal without stripping the pump completely, find a neat fitting rod,(pin punch etc) , insert it in the delivery valve seat and work it to and fro sideways till it frees up and can be removed. Flush out any fragments of the old seal before fitting new one. Use two spanners, (one to hold the valve body) when fitting or removing the injector line, to avoid disturbing the seal once it is seated correctly. Hope this helps, Regards, Combustor.