A few magazines refer to their written idea sources in assigning articles to reliable, experienced writers, or even allow those writers to peruse them for topics to write about.
And for awhile, I kept an idea book that was similar to a writer's journal. But there was a problem. If I needed an idea, I had to virtually read every entry before locating the one I wanted and needed. However, doing this so frequently proved to be a waste of time and energy. But after tweaking it a bit, I found a way to make it more efficient and profitable for me.
I used a looseleaf cover and paper, organizing my journal into a few specific categories of interest, such as "pet health." There, I would include entries that directly related to that topic. For example, I would include observations tracking my progress in helping my cat recover from conjunctivities (pink eye), following following the vet's advice to developing my own strategies for administrating medicine with an eye dropper. I would also include a few notes on what I probably should have done, as well as mistakes I made during that time. Bits of information from relevant, reliable websites and books would be included.
Organizing my observations and notes this way enabled me to quickly locate a given topic and review its entries. Rereading those entries not only refreshes my mind, but provides some material from which to manipulate and gain additional insights for possible articles and books.
In effect, I was writing entries in a writer's journal, but in a more organized manner. No more endless searches and rereading entries for me!
You can try this yourself, using a separate hardcover, stitched notebook for each topic of interest. This strategy is especially effective if your topic or topics are rather involved, motivating you to write detailed entries. Otherwise, a looseleaf notebook is fine. You can change the order of topics from three to two and organize their contents better.
Another suggestion is dating each entry, as well as assigning a title to it. Doing this will save time. Instead of reading all of the entries under a given category, all you'll need to do is read a few selected ones. Dating entries is also useful for organizing purposes, especially if you want to track your progress in moving from idea trigger to a fully developed piece.
And finally, wait until you have a month to several months' worth of entries under various topics of interest. Your subconscious will be at work in the meantime and you will be in for a pleasant surprise when you refer to your idea book again. Remember to keep making entry "deposits!" And have fun.
Happy idea mining!