You could , but the secondary would be a big circular flat mirror with a diameter at least 1/2 that of the main mirror, so the performance of the telescope would be pretty bad compared with other newtonians and cassegrains of the same size.
Take a look at the Parks site (they produce dual fast newtonian/cassegrain telescopes), you can get optical sets of them too.
http://www.parksoptical.com/index2.p...ube+Assemblies
and
http://www.newportglass.com/angwcat.htm are a good source of components.