You’re not crazy. Near as I can tell, the senior-level talent pool is genuinely dry — and it isn’t just developers. Right now, senior-level anything is hard to come by in IT. And even in those companies I do see with senior-level talent, there are often leadership vacuums that — and you might be ahead of me here — cause those people to eventually flee.
Of the senior developers I know, those in need of work are in one of two categories: they’re unemployed, but they want to think deeply about new, groundbreaking problems rather than merely build the latest web app; they’re working at a company they want to leave but are too invested and too busy to make their escape.
The best way I’ve found to meet better candidates is to metaphorically (or perhaps literally) tap on peoples’ shoulders and strike up a conversation. Advertising a position just doesn’t communicate your company’s values and goals the way real dialogue can, and unless you have one hell of a reputation, only direct contact can engage the candidates you’re after and spark their excitement.
Best of luck to you.