How about using the ones from shredder.com? They have new ones every day and they allow you to link them to your web page for free as far as I can see. They might be a nice addition to have on our opening page here at RHP or just have them elsewhere. Here's the link:
http://www.shredderchess.com/chess-news/shredder-news/chess-puzzle-webmaster.html
They aren't usually "find mate in x moves" type puzzles, but are just "find the best move" types. Some are just finding a single move, and some are a series or two or three moves. If you go to their site you can check them out and see what you think!
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Another option would be to see if some of our own members can put together a variety of chess puzzles that could be used for this purpose. Most of us probably aren't that clever, but I'm sure there are a few around here who could do it. The posers and puzzles forum will have some at times, but not on a regular basis.