Have you gone to your post office and asked them i they have IRC's? I've only used them twice myself, but I never got a response back when I sent two requests to the UK. I don't know if they are actually used or not. I think you are correct, though, they probably don't respond if you don't include ...

Hey all, I've got a question, which I hope you can answer. I really want to send a letter to Alexander Skarsgard, asking for a photo with autograph, for me as well as a dear friend of mine. Now, I read you have to put envelops & stamps in your letter, or an "International Reply Coupon"...