Resonant frequency of RLC circuit
I'm trying to find the resonant frequency for this circuit

Try this calculator. I spent a lot of time getting it right LOL: -

The natural resonant frequency you calculated is in radians per second by the way. In hertz it is 80.52932 kHz.

Also according to Hambley, at the resonance frequency the equivalent
circuit impedance is purely resistive

That isn't true from what I can tell.... If you look at this impedance matching calculator on the same basic website it shows at what frequency the input will be purely resistive: -

I've had to frig around to make the numbers match about right with the first calculator but, the upshot of what it is telling you is that the frequency where the input impedance is purely resistive is 50.63 kHz. And, at that frequency, the input resistance is 24.79 Ω.
There are full derivations on that page.