None on the gate, but if you buy through Ticketmaster online (follow the links from the Tattoo site) they will email tickets for your to print! Did this earlier in the week.
One of my mates who lives up that way reckons you may be able to pick them up at Little Chef restaurants. I am not sure whether you can get e-tickets this late in the day now.
I'm also planning the Little Chef ticket thing tomorrow. Check the RIAT website. There's also the Tourist Information/Barclay's bank options on the day, if they have any tickets left and you don't mind queuing to get into the show when you arrive later.