We have a vegetarian restaurant here called Govinda's and I highly recommend if you're ever in Sydney. The meal is a set price per head and it's an all you can buffet of delicious healthy things (and they have a movie room upstairs with cushions and lounges so do the dinner+movie thing if you can).
One of their delicious things is a cauliflower fritter. They are golden brown and crispy and they are out on the buffet table but they stay crispy. I wouldn't say they were ever there for very long, fresh batches are always coming and turn over is quick, but they definitely stay crispier for longer than anything I've ever fried.
How long do you want them to stay crispy for? I find that when I deep fry anything, it will stay crispy for about an hour, depending on how much you fry it. The longer, the crispier. They also keep the stuff heated, though, if it's a buffet, so that helps