Hi,
I don't think here in Portugal is any Club about Military vehicles, but sometimes, off-road clubs organize encounters to only military vehicles.
http://www.clubettoeiras.com/Album%20de%20Memorias%20do%20Clube%20TT%20de%20Oeiras/2007%20-%201%20encontro%20veiculos%20militares%20antigos/index.html
http://www.clubettoeiras.com/Album%20de%20Memorias%20do%20Clube%20TT%20de%20Oeiras/2008%20-%202%20encontro%20viaturas%20militares%20antigas/index.html