I have seen legendary members say that they have a hard time finding posts to merit. In my case it's the opposite, I have less merit than I would like to send. Sometime, seeing a post worthy of merit, I've thought: well, as soon as I get the next smerit, I'll come back to this post and give it a merit.
That exact same thing used to happen to me before I got tapped to be a merit source, and I was earning a pretty decent amount of merits back then, too. But once I (or anyone else) became a merit source, I had both my earned and source sMerits to use, and believe me you get plenty if you're a source.
I do have a relatively hard time finding meritable posts on my own, and I try to use DmdrDmdr's "ranking up" thread to guide me by pointing out members who need merits to rank up. I also think I may have lowered my standards a fraction. My standards for giving out merits used to be incredibly high, but now as long as a post is on-topic, of a decent length, has decent grammar, and is (hopefully) made by a member below Legendary I'll give some merits out. And I do end up meriting Legendaries a lot of times, but I try to give lower-ranked members priority.