Same here. Looks to be an omission in the manual.

After searching GE's site high and low I finally found some pitifully basic instructions which I've elaborated on here.

Bulb required: Manufactured by Aglaia for GE, 130V 35W Halogen bulb GE #WB08X10051 or equivalent.

There is a grille above the door and clock/cooking controls that extends the width of the unit. You need to remove this to get to the light receptacle. With the power to the unit off (unplug if you have access to it), get on a chair with a Phillips head screwdriver. Look down from the top and you will see two screws about 6" in from the ends. If you don't see the screws, open the cabinet doors above the unit (mine were blocking the screw heads). Remove the screws and set aside. Pull girlle towards you at the top being careful not to break the tabs at the position where the screws you just removed are located. After the tabs are out the grille should lift up (there are three hook-tabs along the bottom). Set it aside. Over toward the right you will see a smaller vertical grille. Just to the left of this there is a void with a Phillips head screw facing you. Remove the screw from the receptacle tab. Lift up the receptacle tab on the right. When the receptacle is clear on the right, move the receptacle to the right to release it from the tabs on the left. Lift the receptacle up until it clears the housing it just came from. Pull it gently toward you, rotate it bottom-toward you, and you will see the bulb to be replaced. My bulb was lightly held in using white silicone and removed easily by pulling it in the direction it was pointing. A word of caution about Halogen bulbs: When handling new bulbs be careful not to get any grease on them and handle them with clean cotton gloves or a clean t-shirt. Grease and oils from even clean hands will cause the bulb to burn out quickly. Replace the receptacle being careful to make sure the electrical wires are not pinched by the receptacle housing. Replace the screw; replace the grille; return power to the unit. You're done!

To find the bulb I Googled "General Electric WB08X10051" and "Lamp Halogen WB08X10051" and found options ranging in price from $8.10 to $10.71 ($13.50 with GE).