Sadly, according to jadedsirius there were no letters addressed to you among lupercus's papers, though there was a short note to Neville Longbottom that read simply:

Neville,

You are strong.

-R J L

I've no idea in what context the note was in, or even when it was written, but I thought you might know how to reach Neville and pass it along to him.

As for potions_master, he has only this to say:

Mrs Kerr,

I have absolutely nothing of import to say to you, as you are Muggle and therefore utterly and completely useless. Please find something better to do with your time than pester me for pointless missives. I have work to do.

- S. Snape

...well, you did ask, Peg. ;-)