could try uncomapny
go to parts - marui original parts - look under m1911a1 - those parts should be the same for the housing, but might have different model numbers -- could be gm1-13 on the 1911 model?
worth a look
edit: here are links to the hi capa exploded diagram VS the m1911 - those parts 'look' the same.
1911a1 -
http://i290.photobucket.com/albums/l...rtsDiagram.jpg
hi capa -
http://www.co2airguns.net/collection...%20Diagram.jpg