I'm a little late on the uptake, but I just came across this lovely article on XOJane by Marianne Kirby: "To get a letter, send a letter: where to find a pen pal."
Some of the resources she lists are ones I've heard of and mentioned, but some are new to me, and she does a lovely job of explaining the ebb and flow of letters, and why she always comes back to them. Also, she gives out her PO Box address and offers to write a letter back to anyone who writes to her. Do check out her fine article.
In other news, I suppose it is good news to explain that the reason I haven't been blogging much lately is because I've been writing lots of letters. The 5-year-old son of my cousin is newly a mail devotee, and he writes me almost daily... I've been trying to keep up with him, and sending him letters and postcards almost daily, too! Whew. It's exhausting but exciting work to mentor the epistolary aficionados of the future. Also, his dad (my cousin) is writing letters to me, too (generally in the same envelope), and that brings back some great memories. His dad and I used to write each other pretty frequently, back in the days before email had overtaken the world, and it's delightful to take up that habit again with him. Oh, and I've been trying to keep up with all my other letters, too... though I've long since made my peace with the fact that I'll never really catch up. That's okay. I enjoy trying.