First, welcome!
Well, the bad news first, it's a Craftsman and parts availability is, well, spotty, to be charitable. A once great brand reduced to pity.
It does look like you have a 1/2" collet but the picture could be deceiving. Is it damaged?
For some hope, many of the craftsman routers were made by other manufacturers and you might be able to figure out who made this one. Craftsman archaeology isn't my specialty but there are others that might be able to help. I'd try general routing or router reference subforums. Also, post the exact model number - it should be on a plate on the back of the motor. I'd also try googling the model number to see what pops up.