The best place is the big auction house like Sotherbys. They charge for a quick look but if its original then its worth a lot of money. Not to rain on your parade, it is unlikely that all four or even one maybe original unless you were there at the time. During thr height of thier fame everyone from Prince Charles down to the youngest fan wanted Beatles autographs and they had no choice but to get there roadies to reproduced them. The Beatles sell just as many albums every year as they did when they were going and the liverpool music festival this bank holiday weekend will bring in around 35,000 people. If your autographs are real then you are looking at thousands of pounds- good luck