If it's a "standard" push-pin mount, a MT or Atlas pin will work. Clean the hole out with a 5/64 inch drill bit and replace the pin.
MT trucks come with a bushing for replacing the split pins with MT pins. The instructions are in the package, but all you do is push the busing in from the top, then push the pin into it.
If you take the floor out, you might be able to drive the stuck push-pin out from the top. I have a worn-out pin vise with a piece of 1/16 inch brass rod just for that.