In short, the answer is no. You won't get a reply if you send a letter, no matter how warm, to either the fan club or the management.
The only way to get an autograph is to meet the band, or look on ebay. Personally, I never understood why you would buy an autograph of someone just for the sake of it, it's got no meaning if you didn't get it yourself.
I've only got an autograph of David's. In fact it's more of a drawing - he drew glasses, moustache, eyebrows etc. on Jon's face and signed it

It's a classic, lol! I've got a picture with David and with Hugh, and to me in general having a picture taken together is much more meaningful than an autograph.