I struggle to get flags for my various projects as I tend to be off the beaten track a lot of the time. El CID was a nightmare and I fudged it.
Seven Years War is a bit out there though at least models are available from Crusader and Front Rank, though if like me you love a massive 28mm army expect to be paying you full hobby allowance for a few months!
Anyway I stumbled across a little company called Maverick Models. http://www.maverick-models.com/flags.htm they have loads for various periods.
But it gets better. When I placed my order I got an email saying check what size you want as I can print them to your exact size! So as long as you fall within the parameters you get bespoke flags at no extra charge.
Jason who runs it is very friendly and I am really pleased with the product.
Stevo's Soldiers 