Where can I find collections of chess problems (ideally direct mate) with solutions?

Question

I'm working on a chess program that gives the user various compositions for them to solve. So far I'm only including mate in n problems where 1 < n < 5, and I'd prefer to only deal with this particular type of problem, but the range is flexible.

I'm looking for any sources I can take problems from for my game without infringing on copyright or anything of that nature. The only other requirement is that the problems need to list their solution (ideally clear enough for the layman to understand). These could be sources that are in the public domain or ones that I can get written permission from the author(s) to use.

I've done some searching but haven't found many promising sources. The more problems available the better, but I need approximately 100+ problems in total, so ~33 for each problem type (mate in 2, mate in 3, mate in 4, etc.).

I'm hoping the community here can point me in the right direction.

Answer 1

TheProblemist.org

These direct-mate problems are chosen as a challenge to chess players who may be new to the world of composition. You should try to solve each problem before looking at its concealed solution. It may be helpful to look at the commentary or hints before revealing the solution.

Edit:

Chess.com has a great page of 10 puzzles with interactive chessboards. These are 'checkmate in one move' puzzles though, and are very easy.