You need to stick some needle nose in there and grab the plastic base of the bulb and pull directly up. If you look at the 1st pic I posted, that's the bulb you need. The bulb has sheared off at the base of the glass. It should be a Whelen h50sn12, available from lots of places. They are essentially "pin bulbs" (the second pic I posted) run through a plastic "snap in" SN base, so the base often stays behind. There is also a h35sn12 35watt version that was recommend for smaller rotators when the 50s began discoloring the plastic.
Get that bulb base out and try not to destroy the rotator base, that's the first priority. I wouldn't buy a replacement until you see how the base of the rotator holds up, sometimes the bulb base has become one with the rotator base and it breaks, in which case a replacement rotator will come with a bulb.