It might not be possible to get the DAC port from the error log if the error logs are cycled frequently. In that case you could restart the SQL Server service to obtain the DAC port, but that would probably clear the problem that required you to attempt a DAC connection in the first place! Not to mention peeing off a lot of users if there was actually no problem: they were working merrily away and you just happened to be testing the DAC for your own amusement.
On a clustered instance, the DAC port is dynamically assigned so unless you specified a dynamic port range to be open on your firewall (something that the security folks would be dead against), you'd probably not be able to connect (remotely) via the DAC even if you knew the port number.
The only option left would be to connect via the DAC locally which assumes that you could either get to the server physically or RDP to it.
The scenario I have in mind is where your server is in a hosted DataCenter which is physically and logically (i.e. firewalls, different domain) separated from your place of work........which just so happens to be the scenario I work in. ;-)