It's just the opposite with me - plenty of ideas, just no time to write them.
(I think I've said this before, but...)
Get a calendar and decide what topic you want to cover when - for instance of course you'll want to be covering Mothers, and graduations in April - so block out April.
And of course Fathers and weddings in May. Then, gift-giving in November-December, framing vacation memories in August, and sports memorabilia can be tied into any major event such as the Super Bowl in January, Daytona in February, or the World Series in October. (In fact, you could probably cover the "sport of the month" as there's always something going on.)
Once you get your monthly topics lined up, start keeping a file for each month. Everytime you see an article on that particular topic, put it in that file.
Then, when it comes time to write on a specific subject, you'll already have info on that topic.
The problem comes when it's "crunch time" and you don't have a clue what to say.
Judi's right though, there is difference between writing an article from a "journalistic" view point and a "sales" view point. An article for a newspaper or magazine is a little different than your own customer newsletter - but only a little different. Just use the same idea, but change the wording.
On the other hand, though, only those interested in custom framing are going to be reading the articles anyway - so (think positive) and treat them like your customer anyway!