I think a good venue for this would be the BP Service Centre on Eastlink,
It's 1 km north of Wellington Road has KFC, Maccas McCafe, Coffe, even if they said yes but you can only use the back area Truck parking area , there would be room for Hundreds of cars. It's accessible from Everywhere The Eastern Fwy, The Monash Fwy , The Ringwood Bypass and the Mornington Peninsula Fwy all link to it and It's more central for the Western & Northern Suburbs. I was going to look into doing this myself, but i just dont have the time atm.
I met with a group of my Thunderbird mates there last Sunday for a cruise to Alexandra pub for lunch, the parking area is just huge.
If you dont go ahead with it, come the warmer months I might start making some enquiries
Anyway my 2c worth
Jets Classic & Custom Car Club
Sunday Breakfast 2nd Sunday each Month BP Eastlink Outbound