Here's a site which shows you all the mailboxes in a given zip code. Cross reference that with the Postal Service site which shows you all the zip codes for a given city, and you can find a mail box. So, I genned up a list of mail boxes in 97222 and 97267.
Mrs. Clackablog and I were out of town last weekend, and needed to mail something. Sure would be nice to know how many there were, say, 20 years ago, as I feel there's a lot less mail boxes and mail drops around these days, just like there's a lot fewer payphones these days. There's even a movement to legislate retention of payphones, as one out of 13 households in the US don't have a cellphone, landline or Internet phone.