The source code is compiled into dlls in the bin folder so you won't find it on disk using the pre-compiled release packages of mojoPortal.
Unfortunately there are often bugs in Mono, it has never become stable enough for me to recommend it for any production web site and lately I have not been testing it at all. It is always hit or miss, often it work but there are some bugs but new releases of Mono often break things, some bugs get fixed, some new ones appear, some regressions occur. It has been that way since 2004, every now and then it works reasonably well but with a few minor bugs but often there are major bugs. Sometimes it doesn't work at all, sometimes it works under xsp2 but not under mod_mono.
I haven't given up on Mono completely though, at some point I plan to start testing again but I'm not setup to do it at the moment. They used to release VMWare images of Mono on openSuse and that made it easier for me to setup a testing environment but since Mono is no longer under Novell they no longer make a VM available so it is more work to setup a testing environment.
Sorry that I don't have better news for you.