Flags are easily obtained from mil surplus dealers etc. If there's nothing local to you, try
http://www.astroflag.co.uk for a cheap one or
http://www.newtonnewtonflags.com/fla...nsign_flag.htm for a good qualilty one.
Re the flypast, the best bet to get a service flypast would be to find out which squadrons he was associated with and get in touch with the adj, if they are still current.
If you're after a Spitfire (or similar), the BBMF are probably unable to help as their tasking is set for the year (but worth a look on their website as they publish the tasking and who knows, there might be something passing by that could be diverted). You might get more joy from the Fighter Collection or one of the other warbird firms if they have something in the vicinity at the appropriate time. Ring up Dux switchboard and ask about....