Oase Pond-Air 30 Alternative?

I have used an Oase Pond-Air 30 air pump for wintering my fish over.
The last pump is about to bite the dust and Oase has discontinued the
manufacture of this little rotary vane guy. 1) Does anybody out
there have a Pond-Air 30 you would sell? 2) Do you have any idea
where I might find a Pond-Air 30 new in the box?

Alternatively, what is a comparable pump to the Pond-Air 30? My pond
is about 500 gallons.

Thanks for helping with this.

Charlie